When you’re happy, you enjoy the music. But when you’re sad, you understand the lyrics.
The purpose of life is not to be happy. It is to be useful, to be honorable, to be compassionate, to have it make some difference that you have lived and lived well.
It's so hard to forget pain, but it's even harder to remember sweetness. We have no scar to show for happiness. We learn so little from peace.
Affection is responsible for nine-tenths of whatever solid and durable happiness there is in our lives.
Perhaps it is better to be un-sane and happy, than sane and un-happy. But it is the best of all to be sane and happy. Whether our descendants can achieve that goal will be the greatest challenge of the future. Indeed, it may well decide whether we have any future."3001: The Final Odyssey"
One swallow does not make a summer, neither does one fine day; similarly one day or brief time of happiness does not make a person entirely happy.