Oh man, that drywall dust is the worst. I did the exact same thing sanding some joint compound in a hallway, figured opening a window was enough. Coughed for two weeks straight, and I'm still finding a fine white powder on top of the fridge a year later. It gets in places you don't even use. You really don't respect how much of that stuff is just floating in the air until you're hacking up a lung.
My uncle's sawdust from his garage projects coats everything in a fine layer. It's like drywall dust or even that craft glitter that shows up weeks later. We shrug off these small messes as just part of the job, but then they become a real problem we have to fix. It's funny how often we learn by dealing with the fallout of something we thought was no big deal. What's your worst "tiny mess became a huge hassle" story?