Off-Topic: Predict People Behavior ?

I've been in a lot of thinking lately about can people read or predict other people behavior ? As I am right now playing through people thought and people reaction over some circumstances, but I still cannot find any strong point to make a concrete solution.

I've read several articles on psychologist and also a few tips and trick on how to get to know people better, but there seem lack of information or direction on how a person could be group into a certain behavior. Well to be honest, people heart is the most unique things to learn about.

Yes! we could say that heart is a noun, but heart lead to something more than people could imagine which is feelings. Feeling is not an object where someone could look or touch. Therefore you could never know what is inside someone's feeling.

So for me, psychologist only make assumption on people behavior based on their reading, learning and experiences in life, but the truth is, no one in this world could really make a solid guess on what peoples' behavior are. But still the best way to get to know people is by experiences.