Play should never be allowed to interfere with work; and a life devoted merely to play is, of all forms of existence, the most dismal.
 Theodore Roosevelt, Theodore Roosevelt; an Autobiography (1913). copy citation

Context

“If they would only keep to rowboats or canoes, and use oar or paddle themselves, they would get infinitely more benefit than by having their work done for them by gasoline. But I rarely took exercise merely as exercise. Primarily I took it because I liked it. Play should never be allowed to interfere with work; and a life devoted merely to play is, of all forms of existence, the most dismal. But the joy of life is a very good thing, and while work is the essential in it, play also has its place. When obliged to live in cities, I for a long time found that boxing and wrestling enabled me to get a good deal of exercise in condensed and attractive form.” source