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Ask YC: What have you learned that rocked your world?

42 points by ericb ↗ HN
My question is meant to be open-ended and not limited to programming. My examples:

Meta-programming, in ruby (the power of code that creates code, being released from the tyranny of typing)

Social psychology (Social proof, hacks for relating to people, hacks for appealing to the opposite sex, hacks for reading people)

Economics (Why the minimum wage is damaging, why free trade is good)

84 comments

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tjr
Differential calculus. Lisp. The circle of fifths.
gnaritas
Seconded the circle of fifths, it's a music thing if anyone is wondering.
SwellJoe
For sure on the Circle of Fifths, and the whole "music theory is stacks of thirds, fourths, or fifths all the way down" thing is pretty neat.

But what blew my mind even more in music is that our 12 tone even-tempered scale is arbitrary and only firmed up a few hundred years ago. Everything before that (and for many years after, and in many non-western musical cultures) was written assuming just intonation. Modern electronic instruments have brought just intonation (and all sorts of weird stuff) back into reasonable usage.

aneesh
Mathematical things: A clever geometric proof of the AM-GM inequality, the Monty Hall problem, functional programming.
ericb
Agreed. The Monty hall problem is definitely a mind-bender in a good way. I started with Erlang, but haven't found a project that begged for it yet, though...
CRASCH
That the hack is the architecture.

Architectures are designed to solve the known set of problems at the time of inception. When that problem set changes people try to adapt the architecture to solve the new problem set. Usually this is done through the path of least resistance. The easiest to implement with the least known side effects.

My favorite example: Web browsers were never ever meant to host applications when they were first designed. They can only passably do so today through elaborate hacks. This is why writing a good web application is so difficult and time consuming. These hacks are now well known established parts of what is the accepted architecture of web browsers but they were once hacks and are still hacks.

Similar examples exist all over the place. Design for the future and build for today...

iamwil
Complex and emergent systems. Certain systems can have only local interactions but have global effects. Some effects in nature are not the result of a single cause, but from the interactions of many local parts. One can design robust behavior (though not necessarily optimal) in the global system through only defining local interactions. Many biological systems have this architecture, such as ant colonies, immune systems, and neural networks, and flocks. So do non-biological ones, such as capitalistic economies, traffic jams, and choosing neighbors. The Atlantic's "Seeing around corners" is a good intro to the topic, as well as "The computational beauty of nature"

Sexual selection is the second child of Darwin that people haven't paid as much attention to, but he spent a significant amount of time devoting study to it. It poses interesting questions on the canonical natural selection mechanisms, when mate selection is factored in. When you look at the mating systems of other animals, there's a wide wide variety. From males that care for the young, polygamy being the norm in birds, homosexuality not all that uncommon in the animal kingdom, and factors that affect male:female size ratio. After learning about it, you dismiss arguments people make about how this or that aspect of nature is 'unnatural'. Chances are, they've never looked, and think all mating systems are like human ones.

Quitting the for-loop through functional programming styles. Hello map, inject, and each. Understanding the power of Lisp, and why it has parens everywhere. Understanding continuations are functions that don't return, and you merely chain them together. Still working on monads though.

mdemare
"Understanding continuations are functions that don't return." I've never heard a clearer explanation of continuations!

I remember when I first read a similarly short explanation of Lisp. Suddenly it clicked. It was something like: "All code can be represented as an AST. S-expressions are just serialized ASTs." Only it was better. Lost the source.

PS: I love everyone's comments, keep them coming!

Prrometheus
Emergent phenomena were a big one for me, too. One of my favorite pieces on the topic of economics is Hayek’s: http://www.econlib.org/Library/Essays/hykKnw1.html

Dawkin’s “The Ancestor’s Tale” showed me this pattern in biology, too, and drastically rewrote the way I see the world.

Being able to follow and understand mathematical proofs for the first time was also enlightening. I prefer the simple, clever ones, such as Cantor’s diagonal proof of the uncountability of the real numbers: http://en.wikipedia.org/wiki/Cantor's_diagonal_argument

moog
Differential equations. That the world could be described by calculus was a revelation to me.
ashu
Euler's equation.

That conservation laws follow from deeper symmetry principles (Noether's theorem). Symmetry under translation corresponds to conservation of momentum, symmetry under rotation to conservation of angular momentum, symmetry in time to conservation of energy!

http://mathworld.wolfram.com/NoethersSymmetryTheorem.html

tel
This has to do with the context where I learned Euler's Equation, but I can never separate it from Fourier and (later) Laplace transforms. Those are all so beautiful and mind blowing.
maximilian
I'll second that Fourier transform. The idea that you could represent basically a list of numbers with a sum of sines, or any other orthonormal set is mindblowing to me. Nothing in math has blown my mind as much as functional analysis.
tel
Addendum after the edit period:

Wavelet transforms also go on this list.

bayareaguy
"We can implant entirely false memories"[1]

I also remember being really suprised when I first learned the Central Limit Theorem[2] a long time ago.

That said, Hofstadter's "Gödel, Escher, Bach"[3] probably had the biggest impact on me.

[1] http://www.guardian.co.uk/science/2003/dec/04/science.resear...

[2] http://en.wikipedia.org/wiki/Central_limit_theorem

[3] http://en.wikipedia.org/wiki/Gödel,_Escher,_Bach

dfranke
The Central Limit Theorem... that's a good one. Come to think of it, I felt enlightened by it even despite a teacher who wanted to be an actuary but had to teach AP Stat instead because she couldn't pass her actuarial exam, in addition to all the usual horrors bemoaned in the Lockhart essay that was posted the other day. I suppose that suggests that under more organic learning conditions, it would have been quite exciting.
tel
I don't know that I was surprised by the CLT itself. What surprised me about it was how nice it made everything else. In some sense there are whole books full of theorems which go from tedious and complex to 12-year-old simple in just 3 letters.
michael_nielsen
Fun question. First thoughts: logo (the computer language), the proof of the infinitude of primes, calculus and Newtonian mechanics, general relativity, the idea that thinking is a learnable skill.

It's interesting to me what I've learnt but which didn't make my list: most things related to programming, mathematics, and physics, including quantum mechanics. Generally speaking, most of that knowledge was more incremental.

FleursDuMal
Social psychology was a big one for me too. Cialdini's book Influence gave me a lot to think about.

The role that biases play in my own thinking. Charlie Munger's speech that was on this site a while ago articulates a lot of things I was beginning to realize (http://vinvesting.com/docs/munger/human_misjudgement.html)

I struggled for a long time with procrastination and low productivity. When I realized that abandoning the parts of my life that were not deeply fulfilling (browsing the web aimlessly, refreshing RSS feeds, wasting time in forums, watching tv etc) would not actually be as painful as I thought it would, it changed how I live and work in a very fundamental way.

ericb
That Munger speech is excellent; it's a great summary.
prakash
If you guys like Munger, pick up his book, "Poor charlie's almanac"
kryptos
Quite a long list actually and hard to put in words.... Functional programming in general..especially its roots( halting problem, church's thesisetc...),reading about ENIAC .... small-world problem(miligram) and modelling such networks,beauty of primes and number theoretic algorithms,quantum mechanics. Several books have also influenced deeply...textbooks/sci-fi/cyberpunk...works of hofstadter,stephenson etc....
daniel-cussen
The Selfish Gene.
dcurtis
The Selfish Gene changed my life, along with Phantoms in the Brain By V.S. Ramachandran.
DaniFong
Godel's incompleteness theorems.
hollerith
How did that rock your world?

I'm not asking you to explain the theorems -- I understand them -- just indicate why or how they are significant to you.

DaniFong
In brief, they're mathematical proofs that certain things are unknowable. Mathematics rarely gets so close to theology. And religion is rarely so certain.
hollerith
Oh, so before you learned about the theorems, you thought you could know anything, and the theorems set you right on that point? And somehow that was a theological or transcendental experience?
DaniFong
There's a big difference in the emotional experience of thinking you know something, and actually having proof of it. I think most theists would be similarly amazed by an encounter with a deity.
mercurio
Diagonalization. Undecidability. Arrow's Theorem.
bootload
"... What have you learned that rocked your world? ..."

Mostly about empirical observations about the natural world. One very simple idea while in High School studying physics & chemistry that "the iron in your blood flowing through your arteries is composed of left over bits of exploded starts (Iron)". Another is how little we really observe and notice things. Every week I make a habit of exploring & looking for new things mostly flora or fauna [0] in the bush. It sharpens your observation skills and keeps you fit at the same time. It never ceases to amaze me finding a new variety of insect. [1] Last weeks was a huge fly. [2] Never seen them before. I'm still hunting after a huge flying insect approx: 4-5cm in diameter that I've only seen around 500+m elevation.

[0] http://flickr.com/photos/bootload/sets/72157600203012569/ and http://flickr.com/photos/bootload/sets/72157600195813933/

[1] http://flickr.com/photos/bootload/sets/72157600195955778/

[2] http://flickr.com/photos/bootload/2294889518

tel
To take it up a notch, everything in your body is composed of left over bits of exploded stars.
bootload
"... everything in your body is composed of left over bits of exploded stars ..."

Sort of.

It is Iron with Atomic #26, the 6th most commonly abundant element, that in massive stars where stellar nucleosynthesis occurs is the point where the energy generated through fusion. The binding energy to add a neutron or proton, releases energy. After Iron (Fe56) the binding energy required to add a neutron or proton requires extra energy and can result in a collapse with heavier than Iron elements being generated in a super nova.

While stars up to our sun convert H->He and heavier elements it is Carbon, Nitrogen & Oxygen cycle (especially Carbon) that allows larger stars to create energy and finally the advanced fusion stages required for elements up to Iron. So you could probably argue that the existence of Carbon in humans is the just as significant.

Elements heavier than Iron requires explosive nucleosynthesis or a super nova to be created. These elements have unstable half lives. Hence the importance of Iron. [0]

[0] I've butchered a lot of physics here. Feel free to pick me up on the finer points.

tel
Okay, true, but I'll stand by a "nearly everything" since a very large subset of organic molecules are composed entirely of atoms lighter than Fe. We're probably safe to say that only small parts of your body require more exotic cosmological phenomena for their base material.
mxyzptlk
Girls like sex too.
kajecounterhack
It rocked my world to know why all comments with the word sex in it were immediately upmodded.

Turns out, people really really like sex. A lot.

maestro7
I wonder how many girls upmodded that comment?
maximilian
On this tangent. I think that the moment I realized that nobody thinks as complicated as we think they do. Basically it boiled down to this thought, "If that girl came up to me right now, how would I feel?" "I'd feel great thats what!". And then I get up the balls to go and talk to her. The idea of putting myself in other's shoes really changed my attitude on a lot of things.
sabat
You know what's funny? What you said is true for pretty much everything else in life, too. Not just sex.

Here's something I've learned that rocked my world: most things are not nearly as complicated as I make them in my head. Apparently this comes from some kind of childhood issue with pleasing parents. But if you're smart, chances are you can do a lot more than you give yourself credit for.

I just wish I'd learned that earlier.

mixmax
Darwinism, Evolution and survival of the fittest. Such a simple idea that has such broad implications.
aflag
To talk

To write

Gravity

Newtonian laws

The scientific method

Although only now I'm starting to realize how amazing all those things were. And I took it for granted for all my school years... They were all just means to pass a class. What a shame.

dreish
The thing I'm most thankful to have learned in 2007 is that there is a _lot_ more that I don't know about programming than I thought there was.
mhb
Stack three polarizers. Orient #1 and #2 parallel, orient #3 perpendicular. See no light come through.

Rotate #2 to 45 degrees. See light come through.

Remove #2 completely. See no light come through.

gaika
Most people do not like when I'm telling them about my startup. Especially online. Somehow talking about what you care about is taken as a self-promotion and counts as spam in their eyes. Go figure.
rugoso
hey ericb, can you tell us how you learned social psychology? maybe what books, sites ... etc ?

also im checking the material that FleursDuMal mentioned ;)

ericb
Absolutely. I was a psych major. Another huge thing I learned, btw, was that my persistence (stubbornness, if you ask my wife ;) lets me learn most anything, which is how I came to be a developer.

Instead of how I learned it, I'll point you to some topics in social psych:

Read Cialdini, the psychology of influence.

This doubles for attracting investment and women: http://en.wikipedia.org/wiki/Social_proof

Social skills-the parens are part of the link: http://en.wikipedia.org/wiki/Mirroring_(psychology)

Halo Effect http://en.wikipedia.org/wiki/Halo_effect

Interesting experiments:

http://en.wikipedia.org/wiki/Milgram_experiment

http://www.prisonexp.org/

http://en.wikipedia.org/wiki/Asch_conformity_experiments

If an area I listed here or in the original post is of particular interest, let me know and I'll reply with the specifics of what I meant, or pointers to some info on it.

rugoso
thanks!, supercool! ;)