The bravest heroes are also the most humble.
G-d made the heart of David and his soldiers strong and brave, so they would win in battle against Israel's enemies.
He made the hearts of Rabbi Eliezer and Rabbi Akiva stubborn, so they could traverse the highway from ignorance to enlightenment in adulthood.
They were all sensitive, humble men, nothing in their own eyes.
But G-d put a stubborn courage in their hearts?and that they would not surrender.