If you can't understand why someone is doing something, look at the consequences of their actions, whatever they might be, and then infer the motivations from their consequences. For example, if someone is making everyone around them miserable and you'd like to know why, their motive may simply be to make everyone around them miserable, including themselves.
Well that is an idea. For another example: if you amass an extremely disproportionate number of young, impressionable men as fans and make large amounts of money off them, but not really helping any of them hands on, it can be inferred that this hypothetical person's motive would not be to help these men, but to prey upon and take money from them.