Whoever is slow to anger has great understanding, but he who has a hasty temper exalts folly. – Proverbs 14:29
Great understanding of what? I think the patient person has great understanding of himself. He knows anger only hurts himself. When you harbor anger, you can begin to have it harden to hate. It can affect even your health: you grind your teeth, put great strain on your heart, etc.
The patient person also has great understanding of his circumstances. He knows that anger will solve nothing in dealing with people. It will merely drive them away.
Most importantly, he has great understanding of God. He knows that God is “slow to anger.” To be patient and slow to anger is to exhibit the very life of God in our life.