You may think what you see is what you get but your brain is constantly interpreting everything you see.
You brain fills in blanks that aren't there.
The image on the right is an example of a Kaniza Triangle - your brain adds a triangle that isn't really there.This is an example of a Kaniza Triangle - your brain adds a triangle that isn't really there.
Your brains is trying to make sense of the world around you.
It uses previous experiences and general rules to do so, but occasionally has errors.
This is often seen in optical illusions.
Caption: : "When you look at these two lines the top one looks longer, but if you take another line to the ends of each one, you can actually see that they are the same exact length."
Slide 3
Conclusion
Just because you view something in specific way doesn't mean everyone else will see it the same way you do.
Sometimes if shown correctly you can persuade someone to see something the same way you do.