One of the most interesting areas of study in investing is behavioural economics. While most of the academic research in this field requires a PhD to understand, there are some really useful basic concepts to know about. Herd behaviour is the tendency of individuals to follow the actions of a larger group.
In investing this is best illustrated by buying high and selling low. Think about some of those stocks back during the tech bubble – no earnings, in some cases no product but they built this momentum that saw their price rise and rise until the bubble popped.