Why do you smile?

One day, I was in the lift going from the 20th floor to the basement.
I stood there smiling, as the lift progressed.

At the 13th floor a lady got into the lift.
The first thing she asked me, why was I smiling so much? And what was so amusing?

I gave her a bigger smile! And said, I just like to smile all the while!
And she stared at me, did not speak for a few moments.

At the seventh floor she got out, and said before going,
"I like that attitude! Keep smiling."

And I did.