I learned how to propagate plants, which is much easier than those who've never tried it might imagine.
I learned how to tell the difference between poisonous snakes (triangular shaped heads and elongated, narrow pupils) and non-poisonous (oval or rounded head and round pupils). I also learned how to tell by looking at the scales on a snake's tail. Why is this important? Because almost all snakes are important in the garden and around the home (although people with laying hens would disagree about the chicken snake) and should be left alone. As someone who played with snakes as a child, they don't bother me. But I do know how to be respectful of them and how to let the beneficial ones enjoy their life as much as I do mine.
Note the perfectly round pupil in the Eastern hog-nose snake above. He's a friend.