Joining a startup is not some game roulette where you gave zero information about potential outcomes and just choose randomly one number.
You as an employee have a lot of agency to find the startup to join that you think has potential. If the startups or founders are unwilling to share their thinking then it’s probably a bad sign.
Think about Stripe when they started. The whole story was that most tech and other companies need payments but it’s a hard problem and back in the day we had do merchant accounts. Makes sense, and there is a clear business and maybe as you talk to the team, you are impressed. They raised from Sequoia and other too VCS. Great, sounds like good company. Obviously there are risks. What if they get shutdown? what if PayPal/visa/Google builds this? Maybe the product will suck?
Compare Stripe to something like pet walking startup Wag which also has raised tons of money. Do you think it’s easier to make money by charging % on business revenue or charging % people walking other peoples pets?
There are always risks and unknowns but it’s not a random throw dice which company you join. Probably there has never been a time it would have seemed a terrible idea to join Stripe, at most it would have seemed uncertain and risky. They could have failed too but now they are a $100B+ company, and your employee equity would be worth $1M-100M depending when you joined.
If you join a random startup, you take a random chance. If you do your research and thinking you can increase your odds like you can increase your odds on the public markets. You can also optimize for the team or domain you want to work in, and even if the startup fails, you might have learned something.