Animals never spend time dividing experience into little bits and speculating about all the bits they’ve missed. The whole panoply of the universe has been neatly expressed to them as things to (a) mate with, (b) eat, (c) run away from, and (d) rocks. This frees the mind from unnecessary thoughts and gives it a cutting edge where it matters.

Terry Pratchett (1948-2015) English author

Equal Rites (1987)
    (Source)

Frequently paraphrased:

The entire universe has been neatly divided into things to (a) mate with, (b) eat, (c) run away from, and (d) rocks.