Sort:  

If you don't mind, why is the 'happYness' spelt with a 'Y'? @vcelier.

My 0.01 cent opinion: "Y" = you, because no one else will come to help but yourself. Cavalry is not comming, everybody is busy on their own campaigns.

I may be wrong, but this is just my opinion. Perhaps the director and the script writer design that title like that to tickle our minds and let us think a moment why "Happyness" is spelled with a "Y" and not an "I"- just a wild guess.

I love the movie, it is my inspiration and motivation in life. This movie also uplift me when ever I am down with life struggles.

This is a really interesting way to look at it @clicker - I'm not sure exactly who said it but I've heard the term 'you cannot save anyone without first saving yourself ' - and it reminds me of this. Your true happyness can only come from you first. Agree as well - this is an amazing movie!

From Wikipedia:

The unusual spelling of the film's title comes from a mural that Gardner sees on the wall outside the daycare facility his son attends. He complains to the owner of the daycare that "happiness" is incorrectly spelt as "happyness" and needs to be changed.

@vcelier & @clicker, thanks for the help.

I'll go with the Y=You version.