Are you sure you know what you want?
Like, really sure?
Have you thought about WHY you want it?
There's a problem-solving technique called The Five Whys. When you're trying to get to the bottom of something, you just keep asking yourself, "Why?", over and over again until you get to the root of the problem.
For example: if you're trying to decide to quit your job and start a company.
Q. Why do you want to do that?
A. Because I'm bored at my job and I think a startup would be more interesting.
Q. Why?
A. Because I'm too good at my job and haven't been challenged.
Q. Why?
A. Because I mastered the basics a long time ago, and the job hasn't changed since then, so I've been stagnating.
Q. Why?
A. Because my boss hasn't given me any new assignments or challenging projects.
Q. Why?
A. Because I haven't asked her to, or told her that I'm feeling bored and unmotivated, so she thinks everything is fine.
Now we're starting to get to the real issue. So maybe, rather than quitting your job to start a company, you should actually have a conversation with your boss to find more challenging work to do.
Keep asking Why until you get to the real core of the problem.