According to Aristotle, happiness consists in achieving, through the course of a whole lifetime, all the goods — health, wealth, knowledge, friends, etc. — that lead to the perfection of human nature and to the enrichment of human life. This requires us to make choices, some of which may be very difficult.
Plato believed a happy person is one who has principles and sticks to them. He or she uses and practices these principles in order to become a better person and a better member of society
In her 2007 book The How of Happiness, positive psychology researcher Sonja Lyubomirsky elaborates, describing happiness as :
the experience of joy, contentment, or positive well-being, combined with a sense that one’s life is good, meaningful, and worthwhile.