In: Psychology
Try to think of a behavior with only one known cause. Your task is to identify the behavior and the proposed cause.
A 20 years old boy just lost his dad(known cause). He suddenly shows a bad temper, spending most of the day alone in his room, being unusually quiet(behavior). So the behavior does seem to be in direct relation to the cause we know. Sudden death of the head of the family automatically brings the burden to the guy in the house. This boy, being the elder one, this could be another reason for his disturbed state of mind. 20's is the peak age where one wants to explore career, life, travel etc. Being stuck in this sudden misfortune situation, is over whelming in itself.
Now to identify the behavior, of course most input can be given from the family nemmemb and closed friends about his changed behavior. Yes one can observe him, when he's doing some tasks, whether he's absent minded or not, when someone speaks to him, the way he responds, if he looks directly into your eyes or not. Talking to him directly also helps identifying his behavior change, in case he too is aware about them, he can explain more clearly. His food/sleep pattern needs to be observed as everything is linked in a way.