User blog:Inept Wiki User/Grasping Concepts

There are many magical and scientific concepts which have been featured in one form or another in the Toaru series so far, and likely many more to come. Some of these concepts are simple to grasp, others not so much. A number of occasions have been observed where there have been misunderstandings which have carried forward and spread before being resolved. While trying to get my head around certain concepts and looking through previous instances of misunderstanding, I became slightly curious as to which particular concepts people here have found more difficult to grasp than others.

My question is this:

Are there any concepts featured in the Toaru series which you have had trouble grasping so far?