When I was just starting my warcraft 3 career (btw it didn't last too long), I would occasionally hear or read about some super powerful tactic that is imba and a no-brainer and lets you win everything. So when I actually tried such a tactic and got brutally owned, I was very surprised.
W3 taught me that most of the time even a great advantage does not mean you can defeat another player simply by somehow using it. It means that if you are exactly the same skill as your opponent, you have a slightly bigger chance of winning.
Any hard-tought lessons like mine?