Happiness.

What is happiness?
We all recognize it at first sight, but can't describe it. Why? Furthermore, every attempt to do so is different.

Events begin to happen since our conception and get labeled either as "good" or "bad". Once labeled, they get a weight, relative to its importance.

The "weight" difference between "good" and "bad" events is proportional to happiness.

Happiness is an attitude.
Happiness is a choice.