How we change what others think, feel, believe and do
Reification is the mental process involved in the 'bringing into being' of something. In Gestalt this includes the addition of things which are not in the original image. We may even 'see' the details that are not really there.
You can probably see the white triangle in the image below. For this perception to happen, your mind had to fill in the gaps in its outline.
When looking at the world around us, our minds work hard to fit everything we see into familiar patterns, matching our sensations to pre-existing mental models. We hence may see things which are not really there, or perhaps are only partly there. Our minds are always helpfully, but falsely, seeing and recognizing things, for example when you mistake a stranger for a friend, perhaps because they have a few physical similarities.
A common process in reification is the completion of an outline. To separate and name objects around us, they need a full boundary. The object may be partially obscured so the outline is incomplete, yet we recognize what it is by completing both the outline and other detail.
The word 'reification' is used in other areas also:
In music, particularly jazz, musicians will sometimes leave out 'obvious' notes that the listener will still hear. This can make it appear as if they are playing very quickly or in complex ways.
To create an illusion that convinces others, all you need to do is provide sufficient cues that their minds will fill in the rest for them. This is best done when they are not really paying attention.
To ensure you do not fall into this trap, pay attention to what you see and what you conclude. Think 'What else could that be?'