The Man MakesA man sure of himself does not need you to be sure of him.
Real confidence is quiet. It is not the man selling himself across the table. It is the man who already did the work and feels no need to mention it.
The loud version is fear wearing a costume. It name-drops. It needs the last word. It reads the room for permission to feel adequate. Settled confidence asks for nothing. It has tested itself in private and knows what it can carry. So it can sit in silence without flinching, be wrong without collapsing, and let another man shine without feeling smaller.
The Stoic source
Marcus Aurelius, Meditations 7.59Look within. Within is the fountain of good, and it will ever bubble up, if thou wilt ever dig.
Translated by George Long
The Scripture
Proverbs 28:1, KJVThe wicked flee when no man pursueth: but the righteous are bold as a lion.
The move
Find one conversation where you would normally jump in to prove yourself. Don't. Stay quiet and let your work answer instead. Notice that nothing bad happens.