Days of simple happiness

A lot of my online friends,(well, I seem to have more of them than the real life ones!), have taken the 100 ┬ádays of happiness challenge. Sounded weird to me. I mean, can you really limit the number of days you can be happy, or appear to be happy? What about the rest of the days of your life? Aren’t we supposed to be happy then? Or was I missing the point? Then one of my ‘real life’ friend explained the concept to me.