now if you understand that, then lets say your motor needs 20 amps to run and you have a 20 amp esc, where you'll run into problems is should the motor get an amp spike, meaning for some reason it needs more amps very quickly, which will usually be caused by the prop, and lets say it needs 2 more amps, your esc will probably burn up, but with the little extra amp rating on the esc you shouldn't have any problems and won't hurt anything. in other words, your motor makes your esc work not the esc makes the motor work