In a corporation, you have many bosses: your manager, his manager, etc. In order to succeed, you have to please all of them, and you don't get to choose who they are individually. The only choice you have is whether or not to work at a corporation - when you walk into a corporation, there's the structure above you, and either you accept all of it by staying, or none of it by leaving. You are not your own boss because you can't choose your bosses.

As a consultant with many clients, you can pick and choose your clients on an individual bases. Have a nightmare client? Fire him/her, find another nicer one. Have a nice client? Keep him. You are your own boss because you choose each of your clients individually, not all of them wholesale.

As for flexible hours - once again, same applies. Three months ago, I had three clients, and I was insanely busy. Right now I have fewer, and I have more free time. I could have more clients right now, but I am choosing not to because I want to have more rest right now. At a corporation, you don't choose when there's crunch time, and when there's periods of lull - those are determined by your manager. When you are self-employed, you get to choose when to take on more clients and thus be more busy, vs. when you want to continue working at a slower pace for just one client. At a corporation, you either choose to work, or go on vacation.

Anyway, you sound like you are happy to have a job again with managers above you. Maybe you weren't very good at being self-employed.