If you came face to face with someone who was secretly trying to kill you, what would you do?
Would you act like you didn't know? Would show them some hostility? Would you threaten them?
Those would all be reasonable ways to deal with someone who intends to take your life.
But that's not what the Prophet Muhammad (peace and blessings upon him) did when a bedouin man followed him around the Holy Mosque waiting for an opportunity to kill him.