You win battles by knowing the enemy's timing, and using a timing which the enemy does not expect. - Miyamoto Musashi

"To become the enemy" means to think yourself into the enemy's position. In the world people tend to think of a robber trapped in a house as a fortified enemy. However, if we think of "becoming the enemy", we feel that the whole world is against us and that there is no escape. He who is shut inside is a pheasant. He who enters to arrest is a hawk. You must appreciate this.

el rápido se cansa y no puede llegar a tiempo.

In single combat you must not fix the eyes on the details. As I said before, if you fix your eyes on details and neglect important things, your spirit will become bewildered, and victory will escape you.