If we meet someone who owes us a debt of gratitude, we remember the fact at once. How often we can meet someone to whom we owe a debt of gratitude without thinking about it at all!

Sowing is not as difficult as reaping.

If I work incessantly to the last, nature owes me another form of existence when the present one collapses.

Night is the other half of life, and the better half.

The light is there, and colors surround us. However, if there were no light nor colors in our own eye, we wouldn't perceive such things outside of us.

Only learn to seize good fortune, for good fortune's always here.

A mathematician is only perfect insofar as he is a perfect man, sensitive to the beauty of truth.