This is the ultimate life hack to be in peace, find happiness and be successful in our life. Setting our mental model is very necessary. Brain is like a computer. You can input any data or program it as per you want. Yeah, we can not learn the process of brain 100%. As we have millions of neuron and we human still can't discover the way of work of our brain. So apart from that we can follow some mental model technique to train our brain think better, think positive and all.
A mental model is an explanation of how something works. So if we could learn how are brain think, it's possible to track and let it think the way we want. It may sounds complicated but actually it's not that hard. Let me give you an example. If you want to be a morning person from the next month or set some new year resolution but can't follow that no matter what you try; the first thing you should do is to set your mind to listen to you. If we fail to do that no resolution, no effort will work.
Like, supply and demand is a mental model that helps you understand how the economy works. That's how mental models guide your perception and behavior. So this is the key actually. We can control or catch up any behavior as per we want. But we have to understand that it's not always possible to follow that, I mean this is not a perfect thing. There is no guarantee that it will work for sure. But we can really make ourselves to think in a new way.
If you are a pessimist, don't think that you can not change that. Practicing on it can make us a new person eventually. We can practice to expand our mental model. We can expand the way we think, they way we behave and all.
I hope I make it simple to understand and hope it helps!