Sometimes your joy is the source of your smile, but sometimes your smile can be the source of your joy.
I have read that the secret of gallantry is to accept the pleasures of life leisurely, and its inconveniences with a shrug; as well as that, among other requisites, the gallant person will always consider the world with a smile of toleration, and his own doings with a smile of honest amusement, and Heaven with a smile which is not distrustful — being thoroughly persuaded that God is kindlier than the genteel would regard as rational.
They looked at each other for a moment.

The moment became a longer moment, and suddenly it was a very long moment, so long one could hardly tell where all the time was coming from.

For Arthur, who would usually contrive to feel self-conscious if left alone for long enough with a Swiss cheese plant, the moment was one of sustained revelation. He felt on the sudden like a cramped and zoo-born animal who wakes one morning to find the door to his cage hanging quietly open and the savanna stretching grey and pink to the distant rising sun, while all around new sounds are waking.

He wondered what the new sounds were as he gazed at her openly wondering face and her eyes that smiled with a shared surprise.

He didn't realize that life speaks with a voice to you, a voice that brings you answers to the questions you continually ask of it, had never consciously detected it or recognized its tones until now it said something it had never said to him before, which was "yes."
"Hitchhiker's Guide to the Galaxy"