There are people without legs living in a poorest environment who are happy. And there are healthy rich people who are depressed. Mostly it comes down to expectations. If you expect more from life than you have, you will not be happy and vice versa.
That’s why managing expectations is one of the most underestimated skills. It can be managing your own expectations but also managing expecations of your spouse, colleague or customer.
The simplest rule is underpromise, overdeliver. Usually people do the opposite.