Happiness is different for everyone, but the Harvard Study of Adult Development that began in 1937 found that men who were most satisfied with their lives well into their 80's had these things in common:

1. A healthy sense of humor and a passion for a cause larger than yourself. 
2. The acceptance that life has its ups and downs.
3. Strong and meaningful relationships with family and friends.

“The only things that really matter in life are your relationships to other people,” notes psychiatrist George Vaillant, the study’s lead author.

Source: HOPE Health Letter, November 2010, Vol. 30, No. 11, page 1