An optimist sees the glass of water half full, while a pessimist sees it half empty. Just like that, everyone's perception of reality is different from each other. Some see light at the end of the tunnel while others see a long dark tunnel. Some see a bright beam of hope while others see sharp shadows. Some see the rocking boat kept buoyant by cosmic forces while others see it struggling against them. Perception is a double edged sword, or rather, a multi-faceted pyramid, with each face varying in size, magnificence and other arbitrary factors. So why is one person's perception different from another, or using the example I gave, why is the pyramid of perception like that?
Perception is an entity, complex beyond imagination. Sometimes it makes up the reality itself, while sometimes reality influences perception.
Ill begin with the latter, how reality influences perception. In this case, the reality I am talking about is what the person has gone through, how he was brought up, what decisions he had made and their outcomes. If fate has been kind on him, he starts to expect better and better every time and gets ungrateful for what he has while the one who has tasted dust or knows how it tastes like has the unique ability to see through the smokescreen of tribulations, can see the silver lining. The other case, how perception makes up reality, is when people start to believe and fall for others' opinions, hence becoming a part of a larger group of predominated minds, which keeps getting bigger and bigger until it becomes the de facto platform of perception. The perception of this majority is then unquestionably considered the reality. But some enlightened souls (enlightened through experiences) do not get intimidated by them and dare to perceive against the unity of weak minds and their sanctuary of unified perception.
There you have it, why people perceive contrarily from one another, why ten artists paint the same picture differently and why one person's reality is not similar to the other.