John Piper, speaking at age 49:
“I am emotionally less resilient when I lose sleep.
There were early days when I would work without regard to sleep and feel energized and motivated.
In the last seven or eight years my threshold for despondency is much lower.
For me, adequate sleep is not a matter of staying healthy. It is a matter of staying in the ministry.
It is irrational that my future should look bleaker when I get four or five hours sleep several nights in a row.
But that is irrelevant. Those are the facts. And I must live within the limits of facts.
I commend sufficient sleep to you, for the sake of your proper assessment of God and his promises.”