they don't make good pets

     You may have run into someone who has a "pet theory". A pet theory may be anything from seeing international conspiracies everywhere, to explaining all human behavior away with the label "psychology".  A "pet theory" tends to stick in the face of all evidence to that might refute it. Once someone has latched onto a "pet theory", it can be hard to let go. I suppose this is partly ego--having once thought up the theory, the holder of the theory would have to admit that he or she had been wrong, in order to let go of it. The alternative would be to cling to the theory, and to the idea that it is correct, discounting all evidence that might serve to prove it false--a very bad mental habit. We all have a harder time changing our minds than we do making them up to begin with--so begin carefully, without any theory in mind, and decide based on what you see and hear--not on the basis of an idea with no evidence to support it.