I used to work at a deli and we sold stroopwaffles. A customer told me that if you put one on top of a cup of hot coffee the moisture causes it to fluff up (this is not true, by the way). But for the next year or so I told that to other customers without checking myself. Finally, one customer said "have you ever tried it?" and I was an idiot and said yes. He knew I was lying.

I still lose sleep over that to this day.