I was listening to a wonderful video today by the venerable Thích Nhất Hạnh in which he relays a message that is believed to have been said by the Buddha and can be thought of as quite calmly and succinctly:

“It is possible to live happily in the present moment.”

Relayed by Thích Nhất Hạnh and thought to be said by the Buddha.

I believe this to be from, or alluded to in the Satipaṭṭhāna sutta.