An excerpt from a letter to his oldest son Theodore Jr.
I am delighted to have you play football. I believe in rough, manly sports. But I do not believe in them if they degenerate into the sole end of any one's existence. I don't want you to sacrifice standing well in your studies to any over-athleticism; and I need not tell you that character counts for a great deal more than either intellect or body in winning success in life. Athletic proficiency is a mighty good servant, and like so many other good servants, a mighty bad master. Did you ever read Pliny's letter to Trajan, in which he speaks of its being advisable to keep the Greeks absorbed in athletics, because it distracted their minds from all serious pursuits, including soldiering, and prevented their ever being dangerous to the Romans? I have not a doubt that the British officers in the Boer War had their efficiency partly reduced because they had sacrificed their legitimate duties to an inordinate and ridiculous love of sports. A man must develop his physical prowess up to a certain point; but after he has reached that point there are other things that count more.
In my regiment nine-tenths of the men were better horsemen than I was, and probably two-thirds of them better shots than I was, while on the average they were certainly hardier and more enduring. Yet after I had had them a very short while they all knew, and I knew too, that nobody else could command them as I could. I am glad you should play football; I am glad that you should box; I am glad that you should ride and shoot and walk and row as well as you do. I should be very sorry if you did not do these things. But don't ever get into the frame of mind which regards these things as constituting the end to which all your energies must be devoted, or even the major portion of your energies.