The motivation behind Odysseus to tell a lie to the Cyclops is
That he didn't want them to know their only mean of scape.
Explanation:
First of all, when Odysseus group ends up in the Cyclop's Island they had a vessel, however, they were not really sure about the difficulties they were going to find on the Island. That is why they were very cautious about their words and movements. Because the cyclops could end up killing them or doing something worse to them. That is the reason he prays to Poseidon in the last chance to be helped. Because Poseidon is its creator and he begs him for intervention.
