* The length of the voyage. The voyage was much longer than anyone had expected. The crew was exhausted and running low on supplies, which made them even more anxious.
* The rough seas. The crew encountered some very rough seas during the voyage, which made them seasick and afraid for their lives.
* The lack of land. The crew didn't see any land for weeks, which made them think they were lost. They were also afraid that they would never find their way back home.