Ai (could be wrong)

That line—“RULE FOUR: Consider everything an experiment”—comes from a famous list often called the “Immaculate Heart College Art Department Rules,” originally created by Sister Corita Kent (an artist and educator) in the late 1960s or early 1970s. It’s not from a single “book” in the usual sense but rather from a poster/handout used in the art department at Immaculate Heart College in Los Angeles.

These “10 Rules” are frequently reprinted and discussed in various art and design books. One place you’ll find them in print is Learning by Heart: Teachings to Free the Creative Spirit (by Corita Kent and Jan Steward). That’s probably the closest thing to an “official” book source for this particular quote.