why to not say no to startup?

Paul Graham has written an excellent essay about starting a startup. He illustrated many points which a entrepreneur joggles through..
and I still maintain, one of the single big mistakes many potential would be entrepreneurs do is "not taking the first step of actually starting" the company. Too much time and energy is wasted is thinking about the process and consequences. The decision should be taken and if it is to start, company should be started asap. Failure is not a taboo, as long as you have thought about that as well.