A blunt comment about my dense banana bread changed how I mix now

I brought my usual banana bread to a work potluck last month and my coworker Dana took one bite and said, "It tastes great but it's like a brick, you're overmixing." I was honestly annoyed at first because I'd been making it the same way for 12 years. But I tried her tip, mixing just until the flour disappears, and the difference was night and day. The crumb is so much lighter and it actually rises properly now. I also stopped using my stand mixer for this recipe entirely and went back to a wooden spoon, which felt weird but works. Now I'm wondering if anyone else had to hear a blunt comment before fixing something basic? What's the baking tip someone gave you that you ignored for way too long?