Steven Marcus: Have you ever written to merely improve your writing, practiced your writing as an athlete would work out?
Norman Mailer: No. I don't think it's a proper activity. That's too much like doing a setting-up exercise; any workout which does not involve a certain minimum of danger and responsibility does not improve the body—it just wears it out. ("Craft and Consciousness", reprinted in Pontifications, p. 18)
I have great admiration for Norman Mailer as a writer, even as a thinker. But what he says here seems poorly thought through. For one thing, he forgets the analogy to athletes that Marcus is suggesting. I'm entirely confident that Mailer would not say that Muhammad Ali was engaging in an "improper activity" when he was working out, taking a few rounds with a sparring partner, say, or even just going for a jog. To suggest that a writer's "responsibilities" when writing are somehow more serious than a boxer's when boxing is not just wrong, it's not what Mailer believes. So I'm quite sure he would retract this statement upon reflection.
Then there's the fact he's just plain wrong about working out. It is simply not true that an easy five kilometer run, or some light sparring in the ring, (or practicing your scales on the piano for twenty minutes,) wears the body out. The opposite is true. What wears the body out is to be always engaged in activities characterized by "danger and responsibility". Likewise, it is not good for your style to constantly (or even continuously) weigh it down with the duty or open it up to threats. You can do this for a few hours at most every day, when you struggle to "write for publication". During some periods, you should set this entirely aside and do, yes, some "setting-up exercises", entirely free of consequences.
People who are serious all of the time aren't really serious any of the time.