The Hardest Thing In Programming

I think reinventing the wheel has its place. It has two benefits:

1) You get a better grasp of how the wheel works.

2) You may invent a better wheel.

Of course, that's not to say that I think everyone should start re-writing everything they've ever programmed from scratch, but if we never tried anything new we'd still be using big stone wheels (The Flintstones cartoon comes to mind).