Bram hints at this, but doesn't quite make it as explicit as I would: the thing that distinguishes great programmers is the ability to understand how the pieces interact. Anyone can understand how one piece of code works, even if it's fairly complex. A good programmer can understand how one very complex piece of code works. However, any modern codebase of any significance is impossible for anyone to understand as a single monolithic whole. The key ability is to create a clean mental model of each piece, even if the actual implementation or interface of that piece is nowhere near so clean, and put those models together to understand all the "between the cracks" stuff. That's the key bit of genius behind BitTorrent, for example. It's not that the individual pieces are so special, but that the emergent behavior of those pieces interacting with one another is very beneficial.