The external is the reflection of the internal

It seems so true. The way we perceive the world is through our senses/mind/experiences/ideals. There is a lot of relativity there. When one is happy the outside world looks beautiful/hopeful, but when is down the whole world seems ugly/meaningless. Our state of mind seems to dictate our perception. Two different people with different personalities view the same thing differently. 

It's like a bunch of blind men, each feeling (for lack of a better word) a different part of an elephant and describing an elephant as what they feel. (And often coming to the conclusion that their definition of the elephant is correct). 

So if you want to see a positive world, you need to change your internal mental state accordingly. As many people in the past have told, if you want to fix the world, first fix yourselves.