Why would the hero ever play badly? I mean- why?

Sorry, but I do not understand. Thought everybody played their best all the time. Ofcourse we can make some minor EV- decisions from time to time- but playing badly?

Poker is more than just profits, and I am very happy mormannorman mentioned the fun aspect of poker. If poker gives us nothing than money we should probably quit altogether- or at least for that session.