In my opinion, the hardest question really is when should you throw in the towel?

There certainly are a lot of zombie companies out there with founders toiling away on "bad" ideas with seemingly no hope of success, burning precious opportunity cost with each passing week, month and year.

At the same time, one hears again and again that the successful founders are the ones who don't give up. That success comes from facing down those doubts, shaking the despair and finding a way to keep going even when it feels everyone around you thinks you are going to fail.

I don't have an answer other than to say that for anyone it is a very personal, gut-wrenching decision. If it is no longer worth it to you, then that is your call and I don't think anyone else -- especially someone who hasn't entered the same arena -- should think any less of you for it. Most startups fail after all.

And, I think that is likely close to the answer to the question. The right time to quit is when you no longer believe in the idea, or in your ability it make it succeed, or even that the idea is superior to other opportunities which might be available to you.

I'm not speaking as someone who has had huge success, but as someone who has faced setbacks and doubts, has come close to running out of money multiple times, but has somehow managed to get past those challenges and has become a bit more comfortable riding this crazy roller coaster.

What I've found is that the drive to "find a way", that survival instinct to keep going because you believe at your core in what you are doing -- that triggers creative thinking. And when you open your eyes and look around you see there are resources and people willing to help you that you didn't see before. You see new paths that were not visible before. At least that's been the case every time in my experience. Once you get past the doubt and are determined to find a way, then you find it. I suppose, until the last time, when you don't...

Ben Horowitz described it as "focusing on the road, not on the wall"[1] and that rings very true to me. You can only see the opportunities around you when are able to stop focusing on the wall (impending doom).

I don't believe founders should be guilted into chasing ideas they no longer themselves believe in. There are certainly cases where quitting is going to be the right call.

But human psychology is such that you will want to "flee the danger" and you will see certain doom when there may very well be a way out.

My two cents (if it is worth even that) is to never decide to quit out of fear.

Don't quit because you doubt your chances.

The time to quit is when you no longer believe that what you are working on is what you really should be working on.

[1] What’s The Most Difficult CEO Skill? Managing Your Own Psychology -- http://www.bhorowitz.com/what_s_the_most_difficult_ceo_skill...

EDIT: fixed typo