Symbolism, Imagery, Allegory
The Game of Life
Marcus uses metaphors of game and play to discuss life as a kind of contest—and one that is not easy to win. He assures himself that the practice of philosophy will help him to gain the advantage by making him focus his gaze inward rather than waste energy sizing up the competition:
So do not glance at the black characters either side, but run right on to the line: straight, not straggly. (4.18)
Life is a contest that demands endurance. It's not for the untrained.
Marcus has a preference for what kind of athlete a true philosopher should model himself after. It's not, as you might think, the bold gladiator willing to die a very horrible death. Instead, he chooses the wrestler (7.61) and the boxer (12.9) because they are entirely self-sufficient, capable of conquering with their bare hands. Just as these two athletes stand at the ready to overcome their opponents, so should all good people be ready to tackle the obstacles in their fated paths.
Sport as Diplomacy
Marcus also finds the language of sport pretty handy when he's discussing other potential conflicts in life—and how to limit the harm that might come from them. He reflects that life can feel even more intense than a friendly game gone wrong, but we still shouldn't take it too far:
In the field of play an opponent scratches us with his nails, say, or gives us a butting blow with his head: but we do not 'mark' him for that, or take offence... Something similar should be the case in the other areas of life too: we have people who are 'opponents in the game,' and we should overlook much of what they do. (6.20)
In the game of life, Marcus has clearly learned that he who plays and backs away lives to play another day.