Because it is a game of imperfect information, poker isn't really about a particular pair of holdings, but rather about things like reading your opponent, and whatnot. Slanksy's fundemental theorem of poker doesn't explicitly adress exploiting opponent weakness.

One way to look at it:
You have to play the player, as well as the cards. You bluff more against weak-tight players who fold too much, and value-bet mercilessly against calling stations. So, what your opponent's correct move is, depends on your tendencies, and vice versa.

Another way to look at it:
The stacks go up, and down, but if a player does to much of one thing or another in a particular situation against a mathematically ideal (maximally exploitative game theoretically perfect) player, then, in the long run, said mistake will be costly.

A third way to look at it:
Since human players are imperfect, your opponent's weaknesses can make actions that would normally be costly profitable.