Take heed of critics even when they are not fair; resist them even when they are.
It is sometimes important for science to know how to forget the things she is surest of.
Nothing leads the scientist so astray as a premature truth.
We must watch over our modesty in the presence of those who cannot understand its grounds.
The ideal, without doubt, varies, but its enemies, alas, are always the same.
Falsity cannot keep an idea from being beautiful; there are certain errors of such ingenuity that one could regret their not ranking among the achievements of the human mind.