The question in the title is a quote from the character Tyler Durden in the book, Fight Club. But how much can we know?
How much can you know about yourself if you’ve never been in a fight? – Tyler Durden
And even for men to prefer gymnastic exercises by far to the baths, is perchance not bad, since they are in some respects conducive to the health of young men, and produce exertion—emulation to aim at not only a healthy habit of body, but courageousness of soul…But let not such athletic contests, as we have allowed, be undertaken for the sake of vainglory, but for the exuding of manly sweat. Nor are we to struggle with cunning and showiness, but in a stand-up wrestling bout, by disentangling of neck, hands, and sides. For such a struggle with graceful strength is more becoming and manly, being undertaken for the sake of serviceable and profitable health. – Clement of Alexandria
Clement of Alexandria is under the impression that the gymnasium, including wrestling/boxing can train a boy/man is courageousness of soul as well as physical health.
 Clement of Alexandria, “The Instructor,” in Fathers of the Second Century: Hermas, Tatian, Athenagoras, Theophilus, and Clement of Alexandria (Entire), ed. Alexander Roberts, James Donaldson, and A. Cleveland Coxe, vol. 2, The Ante-Nicene Fathers (Buffalo, NY: Christian Literature Company, 1885), 284.