Integrity

"Happiness is when what you think, what you say, and what you do are in harmony."
-Mahatma Ghandi

When people are divided, they cannot be happy. It reminds me of a scripture that I read recently:
For man is spirit. The elements are eternal and spirit and element, inseparably connected, receive a fulness of joy; And when separated, man cannot receive a fulness of joy."
-Doctrine and Covenants 93:33-34
I couldn't figure out what this scripture was saying for the longest time. I think it's talking about the reconnection of spirits and bodies after the judgement, but I thought of it in this instant because when a person's body and spirit are not connected, he can't be happy.

Integrity is about being whole and acting according to what you believe. This is what brings happiness, along with virtue.