When Palamedes goes to persuade Odysseus to fight the Trojans, Odysseus pretends to be CRAZY.
This is evident in the fact Palamedes set up a test for Odysseus to know whether he was really crazy. He did this by placing Telemachus in front of Odysseus' plough. It was at this point his pretense was exposed.
Odysseus eventually revealed that his pretense to be crazy was based on what the oracle said, that if he went to Troy he would not come back for 20 years
