Starting a company is like base jumping – without a parachute. In fact, to make matters more exciting, a startup requires you to build your parachute while you are freefalling. Once you make the jump, there is no turning back. If you are really good, you will not simply build a parachute, you will craft a hang glider that will allow you fly around, check out the scenery and then pick the time and place for your gentle landing (i.e., an exit either via an IPO or M&A sale).
If you are really good AND really lucky, you will convert your glider into a rocket that will put you into a self-sustaining orbit. If this happens, your venture will indefinitely prosper as a standalone company.