24M, 3 months into a big company, already thinking about going back to my startup…what would you do? (I will not promote)

I’m 24 and pretty early in my career and I’m honestly not sure what I should be optimizing for right now. I’d really appreciate advice from people who are older and have more experience in tech. I graduated from a great university with a physics degree and started my career at a very small startup. I was one of three engineers and had a ton of ownership. I was doing ML/LLM work, data engineering, research, and just generally got to work on a lot of different things. The company was very early stage and there were only a handful of people, so I was around the same people basically all the time. The thing is, I actually really liked the work. I was working 7 days a week at times, but the work itself wasn’t what made me miserable. I liked building things and I felt like I was learning really quickly. I was surrounded by people who were much smarter than me technically, which I thought was what I wanted. But I also constantly felt like I was the dumbest person on the team. I would go into meetings and feel like I had nothing useful to contribute. Sometimes I would say something and realize afterward that I hadn’t explained myself very well. I would then spend a lot of time thinking about whether everyone thought I was incompetent. I started taking normal gaps in my knowledge and normal mistakes as evidence that I didn’t belong there. The CTO was also very intelligent but could be pretty condescending. There were times where I felt like I couldn’t ask a question without feeling stupid. Another engineer eventually left, and some of the reasons were related to the same general environment. There was also a pretty significant rupture with a coworker I had become extremely close with. We had spent a huge amount of time together, both personally and professionally, and that relationship eventually deteriorated. That was a major part of why I ended up leaving. Looking back, I think I was exhausted by being constantly “on” more than I was exhausted by the actual engineering. There wasn’t really much separation between work and life. We worked together, ate together, hung out together, etc. And because the team was so small, there wasn’t really anywhere to retreat to when things got uncomfortable. Sometimes I remember thinking that I just wanted to have a normal conversation with someone where I didn’t feel like I had to prove that I was smart. I ended up leaving and joining a large aerospace/defense company about three months ago. And honestly, the contrast has been pretty extreme. The large company is much more stable. I have good coworkers, much better boundaries, and I don’t feel like I’m constantly being evaluated. I feel much safer asking questions or saying something stupid. I can actually have technical conversations with people without feeling like every mistake is evidence that I don’t belong. But I’m also extremely bored. The work is much less technically challenging than what I was doing at the startup. My team isn’t really doing ML and there is a lot of bureaucracy and slow-moving processes. I feel like I’m being underutilized and like I’m becoming a small part of a very large machine. And I’ve only been here for three months, which is part of why I feel ridiculous even thinking about leaving already. Part of me thinks I should just suck it up and give it more time. Maybe I’m being impatient. Maybe this is what normal employment is like and I’m just accustomed to the intensity of a startup. But another part of me thinks I already know that this isn’t the type of work I want to be doing for very long. I’m 24, and I don’t want to spend several of my highest-learning years doing work that doesn’t really interest me just because it’s comfortable. The complicated part is that the startup is still around, and there may be an opportunity for me to go back. The company has gotten some real traction and is trying to raise a larger round. The technical work is still much closer to what I want to be doing. I would have much more ownership and would probably learn much faster. There is also obviously more upside if the company succeeds. But there are a lot of complications. The fundraising has been delayed multiple times, so I don’t know how much I should trust the timeline. The company is still extremely early stage. The same CTO is there. The interpersonal situation with the coworker I mentioned hasn’t really been resolved. And I know what it felt like to work there before. I also don’t know how much of the environment was just a consequence of being at such an early-stage startup. Maybe things genuinely get better when a company grows. More people, more structure, more separation between work and personal life, more managers, clearer responsibilities, etc. Or maybe the problems I experienced are actually cultural problems that will just become harder to deal with as the company gets bigger. That’s one of the things I’d really like to hear from people who have worked at startups before. Have you seen a company go from 5–10 people to 50–100+ and actually become a healthier place to work? Or do the interpersonal and cultural problems that exist when a company is tiny usually just follow the company as it grows? And more specifically, if you were in my position, would you actually go back to THIS startup given everything that happened? I’m not asking whether you would choose a startup over a big company in general. I’m asking whether the technical opportunity and upside would be enough for you to overlook the existing complications with the people, leadership, fundraising, and my previous experience there. I also keep going back and forth on whether feeling like the dumbest person in the room is actually a good thing. I’ve heard the advice that you should try to be the dumbest person in the room because that’s how you learn. And I agree with that intellectually. I want to work with people who are better than me. I want to be challenged. I don’t want to be the smartest person on my team. But there seems to be a difference between being the least knowledgeable person in the room and being made to feel stupid. I’m trying to figure out where that line is. I also wonder whether I have overcorrected. I went from an environment that was extremely intense and psychologically activating to one that is very stable and comfortable, and now I’m wondering if I’ve gone too far in the other direction. Maybe what I actually need is a third option: a technically ambitious environment where I’m surrounded by people who are smarter than me and can challenge me, but where I don’t feel like I have to constantly prove that I deserve to be there. I guess my bigger question is what someone in their mid-20s should actually optimize for. Growth? Stability? Psychological health? Money? Interesting work? Good people? I don’t know how much of a career setback it would actually be to stay at the large company for a year or two, versus how much I’d regret not taking a high-growth opportunity while I’m young. If you were 24 again, would you take the difficult/high-growth environment even if it came with a lot of discomfort? Would you stay in the stable job and use it as a bridge while looking for something better? And if you had the option to return to a startup where you had already experienced significant interpersonal and cultural problems, would you actually go back if the technical opportunity was compelling? I’m especially interested in hearing from people who have been through this and can tell me what they wish they had optimized for earlier in their careers.