Sincerity does not equal truth, of course.

It is dangerous to be sincere unless you are also stupid.

You can pretend to be serious but you can't pretend to be witty.

To express oneself honestly, not lying to oneself — that, my friend, is very hard to do.

We are what we pretend to be, so we must be careful about what we pretend to be.

You can't be wise and in love at the same time.

La sincérité est une ouverture de coeur. On la trouve en fort peu de gens; et celle que l'on voit d'ordinaire n'est qu'une fine dissimulation pour attirer la confiance des autres.

You can be sincere and still be stupid.

Sincerity! All my life I have been reproved for attempting to use this word, and rightly so because the very notion of sincerity implies a consciousness of one’s self as a circumscribed entity, a ‘single one’ (Kierkegaard) or a ‘unique one’ (Stirner), to be defined and defended, and that state of self-consciousness is itself insincere.

At my age one's got to be sincere. Lying's too much effort.

La vérité ne fait pas tant de bien dans le monde que ses apparences y font de mal.

Le vrai peut quelquefois n'être pas vraisemblable.

You have to understand you cannot have faith and fear at the same time; you can only have one or the other.

MADAME PERNELLE. My dear, appearances are oft deceiving, And seeing shouldn't always be believing.