Anybody or anything may stand between you and knowledge if you are unfit for it.
Worry is a cloud which rains destruction.
You need not wonder whether you should have an unreliable person as a friend. An unreliable person is nobody's friend.
An egocentric pessimist is a person who thinks he hasn't changed, but that other people are behaving worse than before.
If you can turn a murderer into a mere thief, you are making progress.
Effort makes some great men famous. Even greater effort enables other great men to remain unknown.