Civility is not a sign of weakness, and sincerity is always subject to proof.

Presidential inaugural speech (January 20, 1961)
It is so hard to be sincere when one is intelligent! Itís like being honest when one is ambitious.
> Translated by Onoma<
When others asked the truth of me, I was convinced it was not the truth they wanted, but an illusion they could bear to live with.
Don't demand any sincerity from me, Milena. No one can demand it from me more than I myself and yet many things elude me, I'm sure, perhaps everything eludes me.

Letters to Milena
I am not sincere, even when I say I am not
It is dangerous to be sincere unless you are also stupid
Hold faithfulness and sincerity as first principles
A little sincerity is a dangerous thing, and a great deal of it is absolutely fatal


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."