"No man can be a politician, except he be first a historian or a traveller; for except he can see what must be, or what may be, he is no politician"

This quote by James Harrington suggests that in order to be a successful politician, one must initially have a good understanding of history and the world. By being a historian or a visitor, one can gain insight into the past and today, and use this knowledge to anticipate what may take place in the future. This insight is necessary for a political leader, as it enables them to make informed decisions and anticipate the effects of their actions. Without this knowledge, a political leader would be not able to make decisions that remain in the best interests of their constituents. For that reason, Harrington suggests that in order to be a successful politician, one need to first have a good understanding of history and the world.