What's one BBQ mistake that taught you something useful?

A dry brisket, ribs that weren't where you wanted them, a temperature that wouldn't settle down, or dinner that finished hours late—there's usually a lesson in a cook that doesn't go to plan. What happened, what do you think caused it, and what did you change the next time? Include your cut of meat and cooking setup if they help explain the story. If you're still trying to figure out a cook that went wrong, describe it here and we can work through it together. The goal is to help the next person, not judge the cook.