How do you lose your molars?

The permanent tooth is pushing outwards, causing the old, baby tooth to fall out.

However, permanent teeth can be knocked out from injuries and the such.
People loose teeth by either having them pulled out, or some people knock them out by falling over or having a hockey ball to the face. Little children around the age of six may have their baby teeth pushed out by there second teeth (grown up teeth) and normally wobble them or pull them to break the nerves and they fall out and the tooth fairy then comes.