Practical gentlemen hate uncertainty, balancing of probabilities, skepticism or approximation. They have a number of bitterly satirical comments on persons whose minds are so open that their brains fall out. They are bent on getting to a conclusion. – Max Radin, 1937

Thinking in its lower grades is comparable to paper money, and in its higher forms it is a kind of poetry. – Havelock Ellis, The Dance of Life, 1923

Irons rusts from disuse, stagnant water loses its purity and in cold weather becomes frozen; even so does inaction sap the vigor of the mind. – Leonardo da Vinci, Notebooks, 1508