Don't trust yourself or your code
Jared Parsons writes about how Part of being a good programmer is learning not to trust yourself. It's filled with basic but all-too-often-forgotten wisdom about defensive programming. Key bits: "Turn assumptions into compiler errors," "The best way to avoid making bad assumptions is to actively question them at all times," and "1 test is worth 1000 expert opinions."
I also chuckled to see a sidebar disclaimer that said "All code posted to this site is covered under the Microsoft Permissive Lice." I'd heard of parasitic licensing before, but never like this!