Proverbs 25:28 — a man without self-control is like a city with broken walls; anger is the enemy that raids it.

Without self-control — following the gut reaction toward harshness and wrath — a person becomes defenseless. Mike cites a statistic that the number one reason people lose their jobs is not poor performance but bad attitudes expressed toward employers or customers. The 'broken walls' metaphor describes a life that anger can freely enter and damage.