Defend until the North gave up--essentially the South believed they had more conviction than the North and that would win out.
The South had an idea to fight for and believed they could survive on their own. The South relied on their ports and did not have as many supplies as the North but they had something to fight for. The North lacked morale and a mission. It was also believed by some that the South had the right to leave and the North had no right to stop them through military action.
