The Upanishads/Shakespeare nothing is good or bad but thinking makes it so

The Upanishads:

It is said in the Upanishads: ‘I am the Universe.’ If you ask a hundred people as to how they find the world, they are all likely to give different answers. For some, the world is beautiful and the people are good, while for others, the world is extremely bad, and the people are treacherous and sinful. Why the same world is different for different people? It is so, because the outer world is the projection of our inner world. Therefore, the only way to improve the world outside is to improve the world within. While we may not have any control over the outside world, we can change our world within and thus change the world outside.