Can you ever make an unhappy player happy again?

When they stop having the paitience to talk to you.

I've never had them change their mind so far, and every game they look disinterested or complacent. What is my best option?

a) Sell player

b) Play him despite him being unhappy

c) Maybe wait till he gets happy again one day?!

They do sometimes play well despite being unhappy. Its hard to tell exactly how much of an impact it makes on their ability. Either way its annnoying because IRL, a player is not going to just sulk for over a year because you fined him once.