If the highest aim of a captain were to preserve his ship, he would keep it in port forever. Meaning that nothing in life is without risk, every move you make is a gamble. In life you have to weigh the risks versus the potential reward and then determine whether a calculated risk is worth it.
A captain has a duty to preserve his ship whenever possible, but the vessel is used as intended and that carries some risks. Every time a ship leaves port disaster could strike but a captain does not let this stop them from sailing. Instead the captain weighs the risks and potential outcomes and then decides whether to sail or not.