"Breathe through your nose, Olsen!" my high school cross-country coach would yell at me.
I thought he was just trying to punish me. I thought it was some sort of evil lung endurance training. What I didn't know was that breathing through your nose while running is the fastest way to get oxygen to your lungs.
But I thought he was being mean, and ignored him.
Lesson for the day: Don't just tell people what to do. Tell them why.