I would not think that philosophy and reason themselves will be man's guide in the foreseeable future; however, they will remain the most beautiful sanctuary they have always been for the select few.

How was I able to live alone before, my little everything? Without you I lack self-confidence, passion for work, and enjoyment of life--in short, without you, my life is no life. [Written to his wife, Mileva]

Small is the number of them that see with their own eyes and feel with their own hearts.

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.

Great spirits have always found violent opposition from mediocre minds. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence.

Failure is success in progress

The most aggravating thing about the younger generation is that I no longer belong to it.