Do people always behave consistent with subgame perfect Nash

Do people always behave consistent with sub-game perfect Nash equilibrium? If not why?

Solution

A sub game perfect Nash equilibrium is one where there is a Nash equilibrium in every subgame of the overall game. This may be true in theory but will not always be true in reality. So while players in the game maybe doing the best they can give what the other players are doing, this may not be true for every subgame. There may not be a Nash equilibrium in every subgame. This statement is thus false.