Counter Strike: raw aim, how to outsmart opponents, perfect practice makes perfect and if you put enough hours into anything and do it correctly/good, then you can get good at almost anything.

Path of Exile: Taught me about being efficient. If you're repeating the same action 10,000 times, if you can cut even 1 second off each time you do that action, it adds up over time to a significant amount. And then you can try and cut another 2 seconds off...then another second.