Odysseus knew that the boulder that blocks the way out of the cave was too massive for him and his team to move by themselves.
In the Odyssey book, the main character and his fellow sailors found an island where they decided to rest after their long journey. They soon discovered a large cave – the habitat of the giant Cyclops – son of Poseidon. The crew did not know the cave owner, nor were they willing to wait outside to meet him. This was because of what ancient Greeks called Xenia – a hospitality tradition. It stated that anyone should be glad to let a stranger into their home. Having inferred this about the cyclops, the men entered the cave.
Like many other creatures from Greek mythology, the cyclops did not care for the rules of civilized society. So, having found a group of people that invited themselves into his home and ate his food, he decided to kill and eat them. However, he only killed some of the crew and went to sleep. Odysseus was left with an opportunity to kill the giant.
However, the smart leader decided to blind the monster and use his strength to free the remaining men. The enraged Cyclops followed the voices of people. They eventually lead to him hitting the boulder that blocked the only way out of the cave. By blinding the giant, Odysseus was able to let everyone escape the cave. In other cases, it would have become their tomb had they killed the Cyclops in his sleep.