At some point as a kid, I was convinced that no matter how hot the temperature got, and no matter how many layers of clothing I'm wearing, as long as I'm not moving, I wouldn't sweat.
That is to say, if I stood still in the scorching dessert of 120 degrees, and I was dressed for the Antarctic with 5 wind-proof layers of thick clothes, I believed I couldn't sweat.
What outrageous/ignorant/dumb ideas did you have as a kid?