Plato compares the state to an elaborate and expensive ship. A ship, to accomplish a safe and successful journey, needs an expert navigator at the helm, a captain who knows the capacities of the vessel, geography, meteorology, water currents, navigational astronomy, supplies management, and other related matters. An ignorant and untrained person at the helm of a ship would endanger vessel, cargo, crew, and passengers alike. Similarly, Plato suggests, the ship of state needs expert governors at the helm, governors who are well informed about such things as law, economics, sociology, military strategy, history, and other relevant subjects. Ignorant and incompetent governors can be and have been disasters for citizens and states.
Democratic self-government does not work, according to Plato, because ordinary people have not learned how to run the ship of state. They are not familiar enough with such things as economics, military strategy, conditions in other countries, or the confusing intricacies of law and ethics. They are also not inclined to acquire such knowledge. The effort and self-discipline required for serious study is not something most people enjoy. In their ignorance they tend to vote for politicians who beguile them with appearances and nebulous talk, and they inevitably find themselves at the mercy of administrations and conditions over which they have no control because they do not understand what is happening around them. They are guided by unreliable emotions more than by careful analysis, and they are lured into adventurous wars and victimized by costly defeats that could have been entirely avoided. This is how the Republic portrays politics in a democracy: