"Consider the cattle, grazing as they pass you by. They do not know what is meant by yesterday or today, they leap about, eat, rest, digest, leap about again, and so from morn till night and from day to day, fettered to the moment and its pleasure or displeasure, and thus neither melancholy nor bored. [...] A human being may well ask an animal: 'Why do you not speak to me of your happiness but only stand and gaze at me?' The animal would like to answer, and say, 'The reason is I always forget what I was going to say' - but then he forgot this answer too, and stayed silent."

Source: Friedrich Nietzsche (1997). “Nietzsche: Untimely Meditations”, p.98, Cambridge University Press