How come people hear themselves differently than others do?

Answer 1

Because when you speak or even hear a recording of yourself you know what you mean by what your saying.

From a physics point of view it's because the sound is travelling through different material for a shorter distance. When other people hear you, the sound waves have vibrated through the air and diffused somewhat into the surrounding area. When you hear yourself talk, the sounds are traveling at you from outside in the air, and reflected back at you, but also through the flesh of your head, directly to your ear mechanisms. This can make you interpret the sounds differently than another person would when you talk and make you sound different.