Cease Striving

Happiness is the absence of the striving for happiness.
- Zhuangzi

The key to happiness is not to have what you want
but to want what you have.
- Anonymous

Happiness is not something ready made.
It comes from your own actions.
- Tenzin Gyatso, the 14th Dalai Lama 

Happiness is when what you think, what you say,
and what you do are in harmony.
- Mohandas (Mahatma) Gandhi

Resolve to keep happy, and your joy and you
shall form an invincible host against difficulties.
- Helen Keller

You can not find happiness by chasing after it.
Happiness comes from doing what you love to do,
and from being who you truly are.
- Jonathan Lockwood Huie

Further reading:
Simple Pleasures

Choose To Be Happy