Proteus effect
Overview
The Proteus effect (when your avatar changes how you act) is a phenomenon named by Nick Yee and Jeremy Bailenson in a 2007 paper. It is named after Proteus, the shape-shifting sea god of Greek mythology. In a virtual space, participants given tall avatars were more confident in negotiations, and participants given attractive avatars opened up about themselves more actively. The traits of an avatar are said to unconsciously change how people see themselves, and this shows up in their behavior.
Anonymity and the Proteus effect
When you send a question in a question box, as the sender you are wearing the "avatar" of anonymity. Your social roles (student, department manager, parent, and so on) fall away, which can set free a raw curiosity that isn't tied to those roles. It works the same way for the person answering, and someone who is usually not much of a talker can speak freely in a question box.
This effect can continue even after you take off the avatar. The view is that the experience of working up the courage to send a question anonymously affects how you see yourself in real life too, and carries over into face-to-face communication.