I always ask candidates why they want to work at an early stage startup as a developer, and “because it must be fun” is a show stopper.

Being a founder is certainly not fun. The good parts are there, like earning money, interacting with your team and seeing them grow, the first round, the first sale. But the job is quite painful itself.

Please note that not all startups and founders are / want to be funded with billions of dollars. The true story is that you are going to be overworked and fail 99% of times.