What's wrong with having one founder? To start with, it's a vote of no confidence. It probably means the founder couldn't talk any of his friends into starting the company with him.
Founding a company doesn't entitle you to lifetime tenure. Like every employee, you have to earn and re-earn your standing - and companies are pretty unsentimental about that stuff. If you stop being useful, you get quickly shuttled to the side. That said, the Founder does have a distinct advantage that comes with the title, and with that a unique opportunity to contribute. It takes self-awareness, and the confidence to hand over the reins, but it can be a very healthy and productive long term role.