I’ve been thinking about this question quite a bit and have mixed feelings on the topic. Personally, I have numerous reasons for venturing off and will list them a bit later, but I don’t understand why most people start companies. I think the term “entrepreneur” has been glamourized by the media and all of the success stories, especially in the high tech world. What is missing are all of the failures and bankruptcy stories.
Anyway, here are my reasons:
1) Turning an idea into reality – This is really important to me. This is why I’m in the game. I have so many ideas and just want to bring them to market to let the people decide if they are useful. Making that impact is what gets my blood boiling. As an aside, don’t get frustrated if you feel like all of your ideas are taken. So what, do something better than your competitor if you can’t come up with something original. There is a saying (forgot where I heard it), but it goes something like this: somewhere in the world someone is thinking of your exact same idea right now and your next. The moral is that ideas aren’t worth anything. If they were, you would be able to buy and sell ideas. It’s what you do with the idea. People make the idea and ultimately the company.
2) More freedom – Corporations are governed by rules, processes and (my all-time favorite) meetings. Probably much more, but this is what came to mind first. Starting your own company throws all of this out the window. There are no rules and processes. Just get the product out the door and see if people like it. Kind of extreme, but this is what you need to do. You are basically making things up as you go. Time is money. You really don’t have the time to sit and design everything (should do some basic design to avoid problems later), formulate processes and rules. Especially when you are working out of your parents house!
3) Financial security – If anyone tells you they aren’t in it for the money don’t believe them. We all seek to get paid for the work we do. It’s the old risk and reward adage. The more risk you can bear the more reward you can get. Starting your own company is very risky (on average 9/10 businesses fail), but can be very rewarding financially in the long run.
4) Flexibility – This is somewhat of a myth. What I really mean here is to have a flexible career path (see the “Monk and the Riddle”). What I don’t mean is a flexible schedule (which most entrepreneurs say). Well, that doesn’t really fit into starting your own company b/c your hours will probably exponentially increase. I work pretty much every free second that I have – although I’ve been slacking a bit lately with all of these “events”. For every hour you don’t work your competitor will be working. Just keep that in mind. Ok, gotta get back to work now. 
5) No regrets – I don’t want to look back on my life and say “I wish I would have done that, but I can’t now I have kids to support”. This a common theme from discussions with older folks that I have met while working in industry. The fact of the matter is, there is NEVER a good time to start a company. Once you learn to accept that you can move forward.
