Do you have 6 months of living expenses saved? Most startups fail. You should pretty much expect that to happen, which means you should plan accordingly for the economic consequences. What stage is this startup at? Pre-seed, seed, Series A, Series B all have different risk profiles. The smaller the company, the more important it is that you know you will get along with the founder(s), and the more important it is that everybody has a clear understanding of the boundaries/expectations. Some pre-seed and seed companies (pre-PMF) might bounce around wildly through varying product concepts. So keep in mind that the thing you sign up to build might be uninteresting to the market, and you may pivot pretty far away from the idea. The mission you sign up for might not be the mission the market wants to reward. Finally make damn sure you understand how startup equity works. You'll probably want to early exercise if possible, otherwise in the event of success it's very likely you end up with golden handcuffs.

Good points all around. Startup is still forming. I'd likely have some ownership as part of the deal. Investment is an angel investor fronting ~5 mill who'd be paid back at 75/25 rate (25 them). Not sure of exact terms cause they aren't ironed out. I have worked with the other owners before and we're good friends (which could present it's own challenges)

Generally my question is weighing the financial potential of a startup vs that of finding fulfillment in the work