Sauron, dark Lord of Mordor, is a “wise fool.” His knowledge and cunning is great, but he reckons wrong because he reckons only according to his own scales — of power, control, and anxiety. Sauron learns that the Ring is abroad and calculates carefully:

“He supposes that we are all going to Minas Tirith [the great stronghold city of the “good guys”]; for that is what he himself would have done in our place. And according to his wisdom, it would have been a heavy stroke against his power. Indeed he is in great fear, not knowing what mighty one may suddenly appear, wielding the Ring, and assailing him with war, seeking to cast him down and take his place.”