Why you left your job for starting a startup?

In my own company, I get to decide what work I'm doing, what the production schedule is, what the processes are, my working conditions, and so forth.

But mostly it's the "what work I'm doing" part.

The advantage to working for someone else is that there are a ton of things you don't have to pay any attention to. So, when I'm between entrepreneurial projects or am just in a "low energy" period, I work for someone else. Eventually, though, the "itch" returns and I'll start a new company.