I think on the one hand, we all know it would be better to have everything perfectly planned and plotted before even typing the shebang line.

On the other hand, my brain just doesn't seem to work like that. I've tried to organize everything with pseudocode, but I never get very far without actually being in the thick of the code. I'm even surprised when a moderately complicated regular expression works on the first try.

This leads to code that evolves over time and includes lots of quick workarounds that I promise myself I'll fix later. Not exactly the best, most professional way to code, but it's the only one that seems to work for me. And judging by the TODO comments in things like the Quake 3 source, I'm not the only one. :)