Psychology is a subject that I would recommend to everyone. I have learned more things that directly apply to my life in one semester of psychology than the rest of my education.
One thing that was very interesting to learn about was mental disorders. I have always thought of this people as downright crazy and not as real human beings until now. Many can't control their fate in terms of mental disorders.
An example is schizophrenia. Signs for this disorder don't even show up until one is 18-30 years old. Someone can leave a very normal life and be struck with symptoms very quickly.
Understanding these things are very important. It helps doctors treat patients better, and more humanely. Huge improvements have been made over the last century in mental hospitals.