The longing to behold this pre-established harmony [of phenomena and theoretical principles] is the source of the inexhaustible patience and perseverance with which Planck has devoted himself ... The state of mind which enables a man to do work of this kind is akin to that of the religious worshiper or the lover; the daily effort comes from no deliberate intention or program, but straight from the heart.

Imagination is greater than knowledge.

If I had only known, I would have been a locksmith.

Life is like riding a bicycle. If you want to stay balanced you've got to keep moving forward.

The world needs heroes and it's better they be harmless men like me than villains like Hitler

There is possibility in every difficulty.

I never made one of my discoveries through the process of rational thinking