A life without adventure is likely to be unsatisfying, but a life in which adventure is allowed to take whatever form it will is sure to be short.

Bertrand Russell (1872–1970) English mathematician and philosopher

Lecture (1948-12-26), “Social Cohesion and Human Nature,” Reith Lecture, “Authority and the Individual” No. 1, BBC Radio
    (Source)

As collected, with edits, in Authority and the Individual (1949).