Atman consciousness existence, you yourself, is the source of is maximum happiness and everlasting happiness. We normally don't think about it that way. That which we like, we try to get it or keep it. The reverse is also true. If there is something which is giving me happiness continuously, i will never try to get rid of it. It's the reverse of that logic.
"I, the One, illumine this body and also reveal this universe. Therefore, mine is all this universe or indeed nothing is mine." Inspired by this verse from the Ashtavakra Gita, Swami Sarvapriyananda speaks on the nature of the Self.