I think a better way to word this, while keeping the same idea, would be: "In an encounter [if the GM's objective is to run a
verisimilitudinous game] a GM should play NPCs such that they are always trying to 'win', to accomplish whatever goal they have, and use all available resources".
I hope I interpreted what you're saying correctly; I just think the "GM should try to 'win' an encounter" statement carries a meaning you didn't mean to communicate (namely, that the GM is looking to defeat the players).