Problem of other minds
The Problem of Other Minds is a philosophical problem traditionally stated as the following epistemological question: Given that I can only observe the behavior of others, how can I know that others have minds? The problem is that knowledge of other minds is always indirect. The problem of other minds does not negatively impact social interactions often due to instinctive assumptions that others exist, in part explained by mirror neuron functioning. 
It is a major issue of the philosophical idea known as solipsism: the notion that for any person only one's own mind is known to exist. Solipsism maintains that no matter how sophisticated someone's behavior is, behavior on its own does not guarantee the presence of mentality.