No human really has any idea how intelligence works or what it is, but when most people see another human we know that they're an intelligent agent, just like we are. Even if you believe in strong AI, it's not at all clear how to distinguish real intelligence from mechanical imitations, other than the "I know it when I see it" approach we all rely on to recognize fellow humans.
But not everyone. One of the differences between psychopaths, autists, and regular people is that the former two groups can't project their emotions onto others -- they have no empathy. If you ever speak to a person with autism you'll notice that they may pay attention for a little while, and then just wander off without a word. Often, autists will just sit alone in the corner, silently, completely isolated from the rest of humanity. The reason for this behavior is that they are alone, no matter how many other people are around them. Depending on the degree of autism, autists don't identify with other humans or recognize them as fellow intelligences. To an autist, having a conversation is like watching TV: they aren't "interacting" with you. To them, you're no different than a ball or an elephant or a TV character, and if they get bored they just walk away.
Psychopaths are different, and generally much more "functional". They usually realize that the other humans around them are rational creatures, but they still don't identify with them. Psychopaths view other humans like unpredictable animals. Psychopaths may be violent and dangerous, but even when they're not it's impossible to build a relationship with a psychopath; in his mental model you're not the same type of being that he is.
I give these two examples to help explain to you just how different the thought processes of statistical outliers can be. It took me a long time to realize that most people don't think in the same way I do, using the same types mental models and the same decision-making processes. I suspect from what I've read that I share some mental characteristics with Steven Den Beste as far as holistic ("Emphasizing the importance of the whole and the interdependence of its parts.") reasoning and distain for irrelevant details, and I imagine these qualities are present in greater to lesser degrees in all successful engineers. The differences between us and "normal" humans aren't as dramatic as those between normals and autists or psychopaths, but they do lead to frequent misunderstandings and occassionally awkward personal interactions.
Once I realized that most people think differently than me I started learning how to emulate normal behavior, and I think I'm getting pretty good at it. It may sound pretentious or odd to say that I'm often forced to feign interest in the topics of conversation my friends enjoy, but that's not the way I see it.
For example, I wish I did enjoy music and sports, but for the most part I don't. I haven't bought a music CD in over a decade, and I never download music off the internet; I occasionally listen to music on the radio, but only when the talk radio stations go on their simultaneous commercial breaks. I enjoy the experience of going to a concert, but that's not about the music. I almost don't care at all what band is playing.
I rarely watch sports on TV or in person, but I enjoy playing them sometimes. I don't care about teams or athletes, but I follow the Lakers during the playoffs because everyone else in Los Angeles does and it's fun to participate in the conversations.
I don't "look down" on these things at all, I just don't really care about them. To me, they're unimportant, trivial details -- except insofar as knowing and caring about sports and music helps me build relationships with my friends, who I do care about a great deal. So I learn to emulate the thought processes of normal people, and try to act the right way in whatever situation I find myself.
I'd be lying if I said I wanted to be like everyone else. I don't. God made me the way I am, and I quite enjoy it. There are some downsides, but I imagine everyone sees some negatives that flow naturally from the positives they value about themselves. That's just how life is.