Many people will stick out a hand in poker for many reasons when it makes more sense to fold. Knowing when to fold can be just as valuable as knowing how to play the hand. Too many times people stay with a hand because they are already invested in it and this can be a gigantic mistake.
When people want to play the game, they tend to stay with a hand too long and do not fold even when the hand is worthless. As a rule of thumb, people should fold about half the time. You want to play and bet on a hand that is more likely to win than stick with a lousy hand and hope you can make it work out. Sticking out a hand to see where it goes can cost you a lot of money.
Staying in a hand just because you have put money into the pot, does not mean it is a good idea to keep throwing money at the hand in hopes of a win. This is a common problem that new poker players make. When you do this, you are putting money into a losing hand that is likely to cost you more money in the end. It is better to fold the hand as soon as you know it cannot win no matter how much you have in the pot.
Adding money to the final call can also be a mistake. Just because you are down to the end of the hand, does not mean that you should call. If you are at the end and you know you cannot win, it is still ok to fold if the opponent wants to call. If the hand cannot win, do not keep betting on it. This will save a lot of money for you over the life of your poker career.