Funny story. Well, it might not be funny, but I'm in it so it's a chance for self deprecation. Anyways..
For *years* my wife would occasionally comment to me when I'm doing the laundry to make sure I empty the lint trap on the dryer. Simple enough. I've always (99.9% certainty) emptied it, it's just part of my standard routine when I'm doing the laundry. But my wife always seemed to not believe me. This goes on for about fifteen years - "hey, don't forget to empty the lint trap!" "Yep, I always do." "Not always, and remember [woman we bought house from]'s sister." "I'm pretty certain I do, though I might miss it occasionally." "Yeah.. ok."
This one time, fifteen-ish years into our marriage, fifteen-ish years into living where we had our own washer & dryer, she was upset or anxious about something, or in a hurry, or whatever, but she pushed the point further. "Don't forget to empty the lint trap." "Yep, I always do." "No, you don't!" *confused* "Huh.. I do, it's part of my standard process when I'm doing the laundry." "No, you don't!" "I'm sorry but I do it pretty much almost every time." "So why do I find lint in the trap every time I go to put on the laundry?!?" You can see where this is going.
It turned out that we were both correct. The thing was that I had been emptying the lint trap before turning on a new load in the dryer, whereas she always emptied it before taking out the clothes from the dryer. This meant that if she went to do laundry and I had been the last person to take clothes out of the dryer she would find the lint trap full of lint because I hadn't emptied it *yet* - I wasn't going to empty it until I needed to turn on the dryer again. As I've almost always been the one to do laundry, any time she did it the lint trap would almost always be full, so to her it seemed I was never emptying it.
Oh, and I ended up changing my routine to empty it before taking out the dry clothes, matching her routine, as it solved the occasional problem of the lint getting pulled out by the dry clothes and making a mess.