For the first time in my life I began to realize that it is not evil and brutality, but nearly always weakness, that is to blame for the worst things that happen in this world.
Don't argue for other people's weaknesses. Don't argue for your own. When you make a mistake, admit it, correct it, and learn from it immediately.

The 7 Habits of Highly Effective People (1989)
Flee an enemy who knows your weakness
Once we know our weaknesses they cease to do us any harm
The highest point to which a weak but experienced mind can rise is detecting the weakness of better men
The concessions of the weak are the concessions of fear
The cord breaketh at last by the weakest pull


On Anger: "For every minute you remain angry, you give up sixty seconds of peace of mind."
On Destiny: "Our destiny exercises its influence over us even when, as yet, we have not learned its nature: it is our future that lays down the law of our today."
Human, All Too Human
On Friendship: "A crowd is not company; and faces are but a gallery of pictures; and talk but a tinkling cymbal, where there is no love."