Rabbenu Yona explains this a bit differently. He explains that a person should develop an attitude that "nothing is owed to him in life". Then whatever he receives he will have a "good heart" about and will constantly be in a state of happiness. This is based off the verse in Proverbs "A good heart is always in celebration". This is attained through humility. If a person is humble and realizes that nothing is owed to him in life then he won't ever be upset if he is "shortchanged". The root of man's unhappiness is the fact that he constantly feels shortchanged in life. He should have been nicer to me, I should be making more money, I should be healthier, my spouse should treat me better etc. if we can bring ourselves to the realization that nothing is owed to us and everything is really a gift then we will have a "good heart" and be in a constant state of happiness. Many times something doesn't go our way and we console ourselves or others try to console us by saying "there are people who are less fortunate, so it isn't so bad". I think the message needs to be deeper, we need to realize that the guy who is less fortunate is no different than us, there is no reason that we aren't less fortunate as well, what we have is truly a gift. When we were kids our parents always said  "finish your food because there are children starving in Africa", till this day I am not quite sure how finishing my peanut butter sandwich is going to help the starving children in Africa : ) But if we realize that there is no reason that we are where we are and they are where they are, other than the fact that G-d gifted us everything we have, then we will certainly cherish that left over peanut butter sandwich.