This is true in any age because when 'great ones' or important people show signs of madness, it is best to watch them and see what they do next. They could start to make crazy decisions that could cause harm, so it is best to be wary and watchful of them. People not in their right minds could analyze situations differently and more be aggressive or paranoid than a sane person and therefore doesn't react the same as a sane person would. Crazy people in positions of power are unpredictable and dangerous so it is best to keep an eye on them to replace them if things go too far.
Societies keep checks and balances on their "great ones" by not letting them being in power for more than a few years. After a while, the stress and power starts to get to them and affects their brains. It has been found that certain chemicals are released to those who hold office and it affects their thinking and decision making after around ten years in power. Societies have adopted democracies and this leads to limited Presidential terms, with a new President every four or eight years so that the current President doesn't lose his mind while in office.