In the Plain of Illusion, we enter a new world, but view it rather as we did this present one. Although we can create in this world whatever we Will, things are much the same as before in that the apparancy is of a 3 dimensional world. We can create whatever we like and may not be aware of the consequences of what we create.
When we create something, there are other states created at the same time. If we create Victory, then (as someone must be defeated) we create Defeat. At the time, we might enjoy the Victory, but we have also created for ourselves Defeat at some time in the future.
Although we can image our Victory, and also, if we wished, imagine the Defeat of others which is a consequence of this, we cannot simultaneously see the whole effect of what we are creating. We need to graduate to the Plain of Form before we can do this.
The Plain of Illusion allows you to create anything you imagine. When you create something the opposite of what you create is also created. If you steal a sandwhich in the Plain of Illusion, someone will loose a sandwhich.