Of course, this can be traced backwards too; if somebody acts like a cat, then either they perceive themselves to be a human putting on a show and pretending to be a cat, or they believe subconsciously they are truly a cat. For a more practical and realistic example, if you believe you are attractive, then from your point of view that is the truth, but if somebody tells you the opposite, that you are ugly, and your belief is fragile enough, then you will believe them, regardless of how conventionally attractive you are or how others perceive you. Similarly, If I think the best color is yellow and you don't, then that statement is true from my point of view and false from yours- there is no one fact, just many perceptions.
Most people can relate to the second and not the first scenario, as something like believing you aren't human is a rare and extreme delusion, but it works along the same principles as things like self-esteem. However, controlling your inner beliefs isn't anywhere near as simple as putting out energy into the world. Sure, if you spend enough time being told you're the best person in the world you might believe it, and vice versa, if you're told you're the worst person in the world enough times that might be how you see yourself, but if changing your inner beliefs was easy, the cure for depression would be to simply believe you're happy, but becoming happy on the outside and the inside takes a lot more dedication then just a wish, as I'm sure many people can relate to.
So, if you want a better life or just a better outlook on it, then a good starting place would be inner manifestation. Tell yourself things you want to believe every day, maybe during meditation, and eventually you'll start to believe them- and when you believe something to be real, then as far as your perception of reality is concerned, it becomes true.