Human psychology is nothing but study of human mind. By keen observation, we successfully study how humans behave in certain situations. Greed, love, hatred, fear all these are human traits. Psychology studies these. Emotional strength of individuals differ. Psychologists study this. Psychological study enables selection of career. employers also get help from this.
It's a daunting task and we have made sufficient progress over the last few decades in this regard to successfully study human minds with all their mysteries!!
I think Sigmond Freud who is also known as father of psychoanalysis in the world demonstrated in his works the mysteries of minds in a scientific light!
It has been studied truly to a great extent and still the researches are going on.If you visit a Psychiatrist, he asks few questions and is completely able to figure the the root cause of your depression.It clearly indicates that they have in-depth knowledge about the human mind.
Even we can make out our people very easily by taking support of psychology whether our friends or relatives or family members are in problem or depression. It is very easy to know that by their body language, by their facial expression, by their laugh, by their doings, by their way of speaking.