Anyone who has spent time on social media, especially Facebook and other social networking sites, is likely to have cringed at someone revealing far too much about themselves. Overly sexual pictures, comments that would get them fired, inappropriate political rants, and deeply personal details not suitable for strangers are all common online when that same person would never say or do those things in a face-to-face interaction. These sites have privacy controls that allow people to limit the audience they share with, so why do people overshare?
It's not because they don't know how to keep their thoughts private; they choose not to. This results from something called the online disinhibition effect . The concept is simple: people lose inhibitions online that they would have in person. There are six major perceptions that play into this, and some or all of these may be at play at any time on social media:
Anonymity – People can hide their identities. Since their actions can't be directly tied to their actual name or person, they begin to disassociate their online persona with their offline persona. This opens up the possibility that online behavior may be something different that what the person would do in a face-to-face interaction, since it is almost like interacting with two different identities. (I posted about how anonymous comments can be highly disruptive to important conversations earlier on this blog)
Invisibility – Since most online interactions do not involve people seeing one another, people may feel a type of protection. Even if someone's true identity is known (i.e. they are not anonymous), it can be easier to say things from behind a keyboard when the other person (or people) aren't looking at the poster. Many of us have probably experienced this with email. Even at work, we may say things to a colleague in email that we wouldn't say in person.
Incidentally, this can actually help with difficult conversations, since it may be easier to voice important but uncomfortable facts over these "invisible" channels.
Delayed communication – Online conversations generally don't happen in real time. Even chat sessions can have pauses which would never be acceptable in a face-to-face conversation. This asynchronicity means we don't have to immediately cope with something a person says – we can take some time before responding. It turns out this also can lower our inhibitions. We may feel more free to share something personal because we can post it and then leave it, dealing with the reactions later.
Filling in the other person – All kinds of cues are missing in online conversations. We don't hear people's voices or see their expressions and body language. Instead, we read their posts in our own voices in our heads. That can make the conversations feel less real and more like something in our imaginations. Essentially, we might feel like we are talking with ourselves and we lose the sense of the other person involved. That can cause us to say more, since our own imaginations are safe places for secrets.
It's not real – The internet can feel like a place separated from real life, full of characters (not actual people). If we feel like we aren't interacting in a real environment where there are real implications from our actions, it can lead us to drop inhibitions about what we share.
Lack of authority - Speaking in front of an authority figure offline may cause us to carefully consider what we disclose. For example, we may keep many details of our personal lives private from our bosses at work. But online there is equality in what people can post. That can hide offline authority in a way that makes people think the authority itself has disappeared (essentially, they dissociate other people's online identity from their offline identity). If a person does not see the authority in others, they may lose inhibitions about what they share.
Interestingly, there may be technological solutions to some of these issues. Many of them are issues of failing to see connections between the online and offline world. Technology could show that. Imagine a little feature that says "Your boss will see this" (or your mom). Or one that analyzes the text and alerts you when you are about to post something very aggressive. We have the technology to do this and it could be that such subtle clues could be enough to revive some of those inhibitions and cause people to leverage their privacy settings more closely.
 Suler, John. "The online disinhibition effect." Cyberpsychology & behavior 7.3 (2004): 321-326.