The saying you are referring to is often phrased as follows:
"Empty vessels make the most noise."
This proverb suggests that people who constantly boast or try to convince others of their intelligence or knowledge often do so because they lack substance or real wisdom. In contrast, truly intelligent or knowledgeable individuals don't feel the need to brag or show off, as their actions and achievements speak for themselves. The saying serves as a reminder that true intelligence is demonstrated through one's actions, not through empty words or self-promotion.