I worked for 2.5 years at a startup that failed. The technical work that I did was excellent, but it didn't do much for my career in the end. In fact, in my job after that, I was treated as a junior developer even though I was substantially ahead of the level, in terms of capability, at which I was placed. In retrospect, I should have jumped back into the mainstream a year before. As you get older and better, junior-level positions become non-options, but you may not get the "right" experience for senior ones.

Working for yourself can work out very well, or it can leave you re-applying for your old job, 3 years older and 10 years smarter, and you know as well as I do that being 10 years smarter just makes institutionalized life harder.

You can stay corporate and not lose your edge entirely. Obviously, it'd be better to work for yourself and not have to serve 2 masters, but few people have the resources for that. To do it, you have to learn how to be insubordinate enough to keep your creativity, without getting fired. That's not actually hard, if you stay out of the politics. Old Me would react to a pernicious inefficiency by speaking up and loudly, unwittingly walking into a political minefield. ("This is damaging my productivity, you idiots!") New Me says, "This is mildly annoying and reducing my productivity, but that gives me time for Coursera."