The most difficult part of most software projects is the interface between people who have the problem and programmers. Most programmers don't have the ability to handle this part themselves. This is why we have product managers/business analysts. If you can perform both roles, it's amazing how much faster/better the project goes.

Product manager is an imperfect solution to a problem your customer doesn't care about any more than he cares about the name of the obscure sorting algorithm you used to scale his system 1000x.