The line “if you can meet with triumph and disaster, and treat those two imposters just the same” is above the door entering Centre Court at Wimbledon. When I was younger I didn’t understand it, but with the context of the rest of the poem I believe it’s about keeping a level head. When you win you don’t want to become overly confident, and when you lose you don’t want to become depressed or lose hope. Either way, you just keep on going as best you can.