I think the important factors is that at the beginning of a dynasty, the emperor should be a one that cares for his people and want the best for them by providing with whatever they need. They also need to be understanding and patient as sometime building a dynasty is a bit task.
I think that would probably be people who wants to be emperor and would do what ever i takes even if it means killing the emperor or the emperor's son. It could also be that the emperor was very rash in making a decision that led to the downfall.
