It's a circle I've been trying to square recently as part of my career.

Backstory essay: I'm 6 years into my career. I spent 5 of those in the same company - company A, working up from a Grad engineer to an SDE3, 3 promos, in that company. I had a very few stumbles there and always performed and handled transition pretty well.

I jumped ship January of this year over company changes, projects getting cancelled and stopping from a revolving door of Product heads coming in and out. My goal is not to get a senior title but to progress in my knowledge and move on from JS over to a Java focus. I want to build a product or even just some features; I want to code and earn my way to seniority; not start and stop every quarter.

I move to the next company, Company B, in March as SDE; everyone else on the team is Senior SDE with 7+ years experience and above: I'm the most junior.

Company B is a start up and I'm expected to contribute from the off; build out big features and bring some solid knowledge base to the team... but I just totally crap the bed.

The code I write is problematic; there's no documentation to set stuff up, so I go without the code running on my local machine for a while, which obviously causes issues. I make a bunch of amateur mistakes and my direct team lead takes a dislike to me for, naturally, messing up a lot. I go from the guy who can solve the problem and save the day to the guy causing the problem; I'm not trusted at all (and why would they)?

I'm lashed with negative feedback in my first couple weeks, so buck up and genuinely put huge effort in; my code gets better, but the team lead expects tickets closed faster than I can. I feel incredibly untalented and dreadful at my job; every one of my system design choices are the incorrect ones and aren't taken into account. Eventually - right before probation ends - I'm terminated when I fail to complete an MVP of a new system feature.

Obviously, I'd seen the writing on the wall, started interviewing elsewhere and now work at Company C, but as a Senior Software Engineer this time.

Company C is a big company in a bit of a niche area. I'm working on a team migrating from a dreadful old system to a more modern Micro-service base system. I'm expecting to do dreadful and underperform, get fired and end up exiting the industry within a couple weeks.

Instead, I'm back to my old self again: I'm reviewing code with confidence, pushing up solid features, contributing to initiatives and mentoring junior developers again. The code and features I write are solid and passing QA.

There's no tech lead helping me, so I'm just using my gut and it's going swimmingly. I have discussions with the other senior engineer on the team and my technical knowledge is respected; my relationship with my manager is pleasant and I'm performing accordingly.

It's only been a couple months but I feel like myself again; like I went from the back of the herd to the front of the pack... but I'm still so confused about what exactly is the root of my performance increase; or rather, what made me become worse.

Has anyone else ever had this sort of experience, this sort of bumpy ride in their career? Are start-ups hard to work in that larger companies specifically because of expectations, of what's considered "appropriate" at different levels? Am I just a lucky idiot fumbling back in and not even realising?