The Buddha said: “When a person has thoroughly understood the world, from top to bottom, when there is nothing in the world that agitates him anymore, then he has become somebody who is free from confusion and fears and tremblings and the longings of desire. He has gone beyond getting old and beyond birth and death.” – Sutta Nipata
Imagine you knew everything.
That means that nothing is unclear, worrying or unknown. With being free of any fears, confusion or desire you have nothing to think about.
You become truly free. Enlightened.