The factors that lead to overspend/underspend can be categorized into
two: controllable factors and external factors that cannot be easily
controlled. Also, depending on the type of advertising, the reasons
vary. Facebook can have some very different reasons for overspend
compared to Search.For the sake of simplicity, this answer focuses
Search.The attached decision tree will give a good idea of what should
be analyzed in case of an overspend. This flow chart focuses on
controllable factors whic...