I quit my job twice to start companies. Neither made a cent. I read all the YC startup school articles, watched the talks, looked at successful bootstrapped founders and thought "Yeah, that's me! I'll do it!".
Now I am a little older and a little wiser. I realize that I don't have the skills to start a company. Not just tech skills but people skills, sales skills, organizational skills, emotional skills. I think most people, apart from the truly exceptional, shouldn't start a company until they have a great deal of experience. Maybe 40+ is the right time for the average person to start and be successful. Then you have experience, skills, insight, experience and you know yourself well enough.
An aside: I suffer from ADHD. I didn't know when I started my companies, but if anyone reading this has ADHD and is thinking about a startup I suggest be extremely cautious. There are a lot of articles out there that say something along the lines of "Entrepreneurship is great for ADHD! Be your own boss! Be flexible and creative!". It's a bit of a myth. If you don't have your executive function under control while working a job then it won't get any better when you start a company. And mistakes and issues while running a startup will get away from you a lot quicker and more spectacularly than when you are an employee.