The opportunity knocks only once and does not wake up those that are asleep.

Some people are in the habit of complaining about everything; even about the noise made by opportunity that knocks on the door.

The only rule of science is that it has no rule.

I want to write books that only those who read them claim they did.

Solution is always simple once you have the technique.

He is miserable once who feels it, but twice who fears it before it comes.