To Socrates, only a person who could examine every single action and thought had the ability to be in a position of power. Furthermore, Socrates thought that this was the only way to properly live, to live the examined life. If the ruler of a nation leads the examined life, then this would be an example to the citizens to do the same.
However, the problem is that sometimes rulers might have to make decisions that are not philosophically sound. If every single ruler in the world was a philosopher, this might work, but one philosopher-king in the midst of a world of regular kings wouldn’t stand a chance. Rulers have to be more utilitarian in function. they have to think about what is best for the largest amount of people under their rule. What happens when a decision that must be made is in the best interests of the country, but it is not exactly philosophically sound? A philosopher like Kant stated that the only philosophically sound decision in regards to telling the truth was to never lie. But we can all think of situations under which we can think that it would be less moral to lie than to consider the alternative. The only way that philosophers could be effective kings is if we lived in a Utopia, but then how do we reach Utopia without philosopher kings?