"Whoever restrains his words has knowledge, and he who has a cool spirit is a man of understanding." (Proverbs 17:27, ESV)
Restraining your words does not mean you have knowledge. It might just mean you’re shy. A cool spirit does not mean you have understanding. It might just mean you’re reserved. But those with knowledge, those with understanding, always display these characteristics. Their restrained words and cool spirit flow from what they know, namely, that God is in control, working His deep will on the affairs of humanity.
Once you know God is working and in control, once you know this as fact, your words and spirit will be affected. No longer will fret and anger and outrage be your go-to coping mechanisms for that which exasperates. Instead, you’ll demonstrate a calm, understanding the God of the universe sees the groaning of that universe, and the groaning of human souls, and is working in the background to bring about His glorious kingdom. The affairs of man are corrupt, but God's are clean, and the person who knows and understands this has a calm about them that only comes by knowing the final score before the end of the game.