'if this isn't nice, what is?'

One of the things (Uncle Alex) found objectionable about human beings was that they so rarely noticed it when they were happy. He himself did his best to acknowledge it when times were sweet. We could be drinking lemonade in the shade of the apple tree in the summertime, and Uncle Alex would interrupt the conversation to say, "If this isn't nice, what is?"  
So I hope that you will do the same for the rest of your lives. When things are going sweetly and peacefully, please pause a moment, and then say out loud, "If this isn't nice, what is?" 

From a commencement speech by Kurt Vonnegut, discovered thanks to the littlest.

(And it is worth saying even when things are not so peaceful. For example, when movers are in your house with screeching tape, ransacking your kitchen cabinets and answering cells that ring with the theme song from Halloween, and you are sitting on a bare mattress next to your favorite person, who is making you laugh with the world's worst puns.)