This above all: to thine own self be true,
And it must follow, as the night the day,
Thou canst not then be false to any man.
- from Hamlet

Doubt thou the stars are fire;
Doubt that the sun doth move;
Doubt truth to be a liar;
But never doubt I love.
- from Hamlet

There is nothing either good or bad, but thinking makes it so.
- from Hamlet