If you think there are no new frontiers, watch a boy ring the front doorbell on his first date.

You probably wouldn't worry about what people think of you if you could know how seldom they do.

You probably wouldn’t worry about what people think of you if you could know how seldom they do.

We probably wouldn't worry about what people think of us if we could know how seldom they do.

Whoever you think can beat me, just put them in front of me and ring the bell. I talk with my fists.

If you realize you aren't so wise today as you thought you were yesterday, you're wiser today.