Humans have emotions, something robots don't. According to Google, "Psychology is the scientific study of how humans behave, think and feel." When robots don't have emotions, the can't think for themselves. They are pre-programmed - they are told what to say and/or do.

 

When humans aren't connected to each other emotionally, they tend to have "abnormal development" and have a hard time relating to others. Us humans have a need for relatedness, so those who can't relate with others might have odd behaviors. 

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Robot's don't have emotions yet. So, for right now, even though they can try, robots probably can't take over the job of psychology because they can't relate to humans on an emotional level.