To me the fascination with reflections, especially in windows and mirror, is their intangible yet realistic nature. They are like how we all seem to think and reason. At first, glimpses, ideas or perceptions seem unreal, abstract or fragmented. However, as we look more or think and make connections, the unreal and disjointed takes form and the connections are made and what was once of no particular form takes shape and becomes a new reality for us.

I guess that's why we say we are 'reflecting' on something when we are taking time to think.