The Presidency is a lonely job and highly dependent on the advice of experts. Unlike parliamentary democracies, the President is both head of state and head of government. Is this more than anybody can handle? Is anybody ever really prepared for this awesome responsibility?
There are at least three points to be made here.
First, it is somewhat inaccurate to say that the President’s role as head of state makes his (or someday her) job much harder than it would be if he were only the head of government. The job of head of state is a highly symbolic one that does not require a great deal of preparation, effort, or knowledge. It requires a president to look and sound sympathetic to the plight of people in hard times. It involves representing the country at some important ceremonial events (such as funerals or inaugurations) around the world. These are not onerous tasks. Therefore, the added role as head of state is not that much of an added burden.
Second, the US presidency is not all that different from the British parliamentary system in this regard. While the Queen is the head of state, the Prime Minister is still acknowledged by all as the leader of the country. The Prime Minister, in essence, has to act as head of state in many situations since everyone knows that the nominal head of state is only a figurehead.
Third, the presidency may be an awesome responsibility, but it is not much more overwhelming and impossible than many other jobs. The president does have responsibility for promoting the well-being of many people. Of course, the president cannot do the job alone. But there are many jobs like that. The heads of companies have jobs where they cannot possibly attend to all the details on their own. Therefore, they have to delegate tasks and rely on subordinates. The President does this too. The job is hard, but it is not superhuman unless we think that the President is going to micromanage every decision about everything that happens in the country.