This is a summary of some of the key points from kant.

To be happy is to attain a mean between virtues, morals, pleasures, and goals. There are two kinds of mean. The first mean is arithmetical and it is the same for everyone, and is according to entity itself. The second mean is ethical and it is not the same for everyone. It is according to us. If a person can learn to find a balance and become satisfied with his situation as a result of …

…reason. In order for anything to be good the "good will" has to be present. Kant believes self interest doesn't take you in the direction of "good will". What separates the "good will" from everything else is that it is without qualification. Kant states that happiness is good with qualification only if the "good will" is present. Aristotle would bring up the question "are you happy?" Kant would say "are you worthy of your happiness.