Part of the rationale for why this occurs is that the absence of another person judging and reacting to the speaker's words as they type makes it easier to disclose personal issues. Anecdotally, many people who use instant messaging systems (such as AIM or MSN) are able to talk about more personal issues even if it is to someone who they know in real-life. In both cases, the asynchronous nature of the communication channel as well as the absence of another person who judges the speaker instantaneously, with a full repertoire of facial expressions, probably makes the speaker feel more comfortable with disclosing personal information. This is supported by both anecdotal information as well as survey findings.

I'm not sure why I am such close friends with my EQ buddies. I do know that my EQ relationships are better than most of my relationships in RL. I think this is because when you are talking with someone on-line it's easier to talk about certain things since you don't have to look at a person face to face. [m, 15]

It is amazing how much complete strangers are willing to reveal about their personal lives. I believe that the anonymity might make them more bold. [m, 28]

In a conversation between two individuals, as soon as one side offers a piece of personal information, it creates a kind of debt that encourages the other side to do the same. This process is known as reciprocity in psychology. When someone offers us something, we often feel somewhat obligated to return that favor. In the case of disclosure of personal information, the initial tidbit often sets off a chain of increasingly personal exchanges. The ease with which this information exchange occurs allows it to happen earlier and more often than typically in a real-life relationship.

The Cleric I know only what he tells me. But if I ask, he answers. We are very open and trust each other. I mean it's great stress relief to tell someone who doesn't know the people you know stuff about them ^_^. We have spent some nights in dungeons waiting for people or spawns chatting about our lives, what we want to do, and so on ... [m, 20]

A lot of times when people are burdened with something that is troubling them, they can feel better if they can tell someone about it. The problem is that this is not always possible in the real world. The anonymity of online environments makes it easier for a lot of people to share their personal issues, because oftentimes the very people they might turn to in real life are part of the issue itself. Another reason why the anonymity helps is because it removes any fear of repercussions. A teenager who is unsure of his sexuality is highly unlikely to share this information with his friends and family. A husband who is experiencing difficulty with his spouse might be able to talk about the problems with an online friend without fear of aggravating the problem in real life.

I would say its easier to open up to a person whom you are only writing to and never have to face in RL, I can discuss issues with some of them without worrying that that they will tell my other friends about it. [f, 19]

It's easier to communicate without getting uneasy about the usual "is he going to tell anyone what I'm saying?" thing [m, 15]

Of course, this is not to say that everyone who plays an MMOPRG will share their personal lives with their fellow players, but in general, people are more likely to disclose personal information online than in real life for the reasons mentioned. But beyond a higher tendency of self-disclosure, other factors facilitate the formation of online relationships.