Likutei Moharan, Part II 43/ליקוטי מוהר"ן·תנינא מ״ג

1The heart’s meekness causes it to be beset with fears.

2The mighty person is afraid of nothing, and strength is mainly in the heart. In other words, whoever is strong-hearted is not afraid of anything. He charges into the thick of the battle and is victorious on account of the strength and courage of his heart.

3And the reverse is also true. The fainthearted are fearful. This is as it is written (Deuteronomy 20:8), “the man who is fearful and fainthearted.” Rashi comments: “who is fearful”—he is fainthearted, and therefore is afraid.