When You're Smiling

When you’re smiling, when you’re smiling,
The whole world smiles with you;
When you’re laughing, when you’re laughing,
The sun comes shining through.

But when you’re crying you bring on the rain,
So stop your sigh – ing, be happy again.

Keep on smiling, cause when you’re smiling,
The whole world smiles with you.

Words & music by Mark Fisher, Joe Goodwin & Larry Shay, 1928

I like the versions sang by Billie Holiday and the one by Louis Armstrong.
Isn't it the lyris nice and simple? You can listen to it when you feel blue.