It's not a question of happiness, it's a requirement. Consider the alternative.
First rule of Economics 101: our desires are insatiable. Second rule: we can stomach only three Big Macs at a time.
Drive slow and enjoy the scenery - drive fast and join the scenery.
Being sorry is the highest act of selfishness, seeing value only after discarding it.
We may not always get what we want, but surely we will get what we deserve.
Seeing the light is a choice, not seeing the light is no choice.