The mind never need stop growing. Indeed, one of the few experiences which never pall is the experience of watching one's own mind and how it produces new interests, responds to new stimuli, and develops new thoughts, apparently without effort and almost independently of one's own conscious control.
Gilbert HighetMany of the snarly bad-tempered teachers whom we remember with hatred were really nice people soured by years of anxiety and penny-pinching.
Gilbert Highet