What’s the last thing you trusted that turned out to be wrong?

I mixed a live set yesterday and swore the delay on the kick drum was just right. Turned out it was my headphones playing tricks — I’d left the EQ tilted from an earlier session. The whole mix felt off, but I didn’t catch it until after. Now I’m paranoid about trusting anything I hear in the moment. What’s something you believed in good faith that later cracked under its own weight?