Each of us have different story in life some are unhappy because no meny ,some are unhappy in they lovelife ,some are in family problem ,some are in work problem and etc thats why i can say that we have different problem and each problem have solution . but for me life is like a lock you cant open it without a key..
Based on my experienced, People are unhappy because of the following:
1. Different problems like you said.
2. Lack of Money
3. Rejection
4. Not Contented for what we have.