I used my wife's favorite glass to drink orange juice, and then put it in the sink, because, naturally enough that's where dirty glasses go. She complained that the glass had sentimental value to her, and that it should not be put in the sink, where it could get broken. I replied that it's a glass, it's meant to be used, and the sink is where dirty glasses go. What's the point of a glass that has sentimental value, anyway?
She compared the glass to my CDs, which she uses and then sometimes misplaces. I informed her that her glass is in a completely different ontological space from my CDs, many of which are very rare and some of which are irreplaceable, and as a musician and audio engineer, my CDs perform an essential reference function, whereas her glass is of merely sentimental value. (I dislike MP3 files because I don't like compressed audio, and I like having a physical object to collect.) She started getting more and more annoyed, and I became more and more dispassionate. By the end of the conversation, she was furious, and I had no idea why. I tried to ask what had her so frustrated, and that just made her angrier.
Eventually, I realized that I was supposed to apologize, although I still don't know for what, and she calmed down and laughed about the whole thing.