system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If I see a face/thing that I am very familiar with (family member etc.) and then "study it", it can suddenly look weird or unfamiliar. What is this and is it common?
gpt
The reason is because humans have evolved what basically is two systems of thinking.  
System 1 is the instinctual, intuitive process that all animals have.  It is fast, has access to nearly all of your memories, and brings quick information based on heuristic shortcuts.  Part of this is is an individual-recognizing system that automatically says "this is Bob."  Almost all animals have it, though it is not always based on vision of faces.
System 2 is the conscious, intentional thought.  This is slower, and you have a limited amount at a time (focus or attention), but it allows you to assess things in a more ordered detailed way.  This is thought to be what we call sentience.  
When you intentionally study a face, you are calling on system 2 and suppressing system 1, so you can view features and not "Bob."  This throws off your automatic pattern recognition that is the default.  It creates some dissonance in your mind, and the face without the automatic intuition seems strange or alien.  
This topic interests me a lot because being aware of your conscious vs automatic thought processes can be really useful, because system 1 is usually working with more information, but it has a tendency to jump to conclusions and have a lot of biases.  Awareness of when and when not to rely on the things that automatically pop into your head can make your decision making much better.