[b]From a MD perspective...[/b]
Everyone's (all people's, not everyone) mind is a cube and is held exterior to the body. Many small wooden cubes have been said to litter the carnival of Marind Bell. They are all the same shape, although they may differ in size, colour and apparent material.
The minds perhaps share the same thoughts, but people will act on different thoughts because it depends which one 'catches the eye'; which one is concious against the others being unconscious thoughts. The upbringing and environment of the person is the deciding factor as to what thoughts are concious (on the surface).
The mind develops as the person ages and is constantly changing. On the outside of the cube this is not always apparent although changes in size colour and apparent material have been noted.
The inside of the cube contains the memories and experiences of the person. The persons ability to hold memory and not forget it, is dependant on how full the cube is of unwanted memories and experiences and how many candles you left burning.
It has been known for people to be drawn into their cubes when in a state of mental unrest or overwhelming guilt. When this happens it is possible the person may die from the challenges they find there.
[b]Disclaimer: [/b]Do not take the above text as true, it is completely unscientific and is a fiction based on my characters experiences in MD.