The phrase "full of oneself" refers to a person who is overly confident, arrogant, and self-absorbed. To describe such individuals using antonyms, we may use words like humble, modest, unassuming, self-effacing, or selfless. A humble person is someone who shows a modest and unpretentious attitude towards others. They are not arrogant or boastful, and they do not flaunt their successes. Modesty also suggests a genuine lack of arrogance or conceit. Unassuming describes someone who is not pushy or assertive, and they don't try to show off or attract attention. Self-effacing individuals are modest and shy, and they do not like to draw attention to themselves. Lastly, a selfless person lacks selfishness and is interested in the well-being of others.