Be gentle to all and stern with yourself.
Problems are not stop signs, they are guidelines.
Well done is better than well said.
What you do today can improve all your tomorrows.
The dog that trots about finds a bone.
It's always too early to quit.
The secret of getting ahead is getting started.
Either you run the day or the day runs you.
The wise does at once what the fool does at last.
By failing to prepare, you are preparing to fail.
As for everything else, so for a mathematical theory: beauty can be perceived but not explained.