A caveman may fashion a particular spear tip better than the rest and say to himself, "I like this spear, this is a good spear."

"What is art?" There may be no work which so embodies this question as Marcel Duchamp's 1917 work, Fountain.

In the past year I have set about starting a director's journal, a space where I can write down lessons I have learned over time concerning filmmaking. These...