Retro, I think you're the first person I've come across who knows about and likes xkcd but hasn't read them all. Usually the ones know and like it lose a weekend to going back through all the archives. Or maybe it's just the crowd I run with? I know that's what I did with Achewood, xkcd, Dinosaur Comics and Perry Bible Fellowship (in that order). Only I'm still not caught up with Dino Comics because T-Rex is SO VERBOSE. And that dromiceiomimus has a really hard to pronounce name, so it mentally slowed me down for the first several hours... until I looked up how you are supposed to say it. I just started reading them daily from when I discovered them and when I have big chunks of time, I go through systematically from the beginning.
But I digress. This one is my favorite xkcd of all time and it also makes you think, only in a more pithy way: