Deception is part of every relationship, online and off.
The recent case of Manti Te'o and his nonexistent girlfriend has generated a fair amount of discussion, most of if focused on the question of whether Manti was duped or a willing participant in the hoax. We may never know the truth regarding that particular question, but one thing is clear: This sort of hoax is not uncommon, and it cries out for some sort of explanation and understanding. How can people fall in love with someone they never even met?—indeed, someone that never even existed?
First let's be clear that if Manti was the innocent victim of an Internet hoax it wouldn't be that unusual. The MTV show Catfish is dedicated to the task of determining whether someone's virtual love interest is legitimate or a hoax (and the show's producers have no shortage of cases to investigate). On a personal level, I have a friend that fell victim to this sort of deception, and the teenage son of another friend was also taken in by someone pretending to be an online love interest. Like Manti Te'o, both of these people were attractive and would be considered legitimate "catches" in the dating world. I don't know that they could have as many options as a football star like Manti, but they had more options than any one person would need. So why would they fall for simulacra?
One thought is that when we engage with someone online, the information we get from him or her is low bandwidth and it is open textured, meaning that it is incomplete, vague, and ambiguous. By contrast, when we meet someone in real life we take in a tremendous amount of information about how they appear, how they carry themselves, how they speak, dress, etc. Electronically mediated communication carries a lot of information, but it is clearly impoverished compared to what we can get from first person contact. When the human mind receives incomplete information it doesn't perceive an incomplete canvass—it fills in the blanks. From an evolutionary perspective this makes perfect sense. We want to perceive predators and food sources in conditions where we have incomplete perceptual information. But in some cases we fill in the blanks incorrectly and in other cases we engage in a kind of wish projection.
I have seen the Facebook chat logs from one victim of Catfish-style deception, and to my eyes the record was surprisingly spare. There was just too much missing from the communications coming from the deceiver. Of course the victim didn't see it this way; he was filling in the blanks himself and that is what made the connection so powerful—the deceived could project anything he wanted, and he used the open canvass to project the kind of partner he most desired. Of course the hoaxer played along, letting the victim paint whatever picture he desired and affirming that picture at critical junctures.