What you think you become is a famous phrase that was said by Buddha. What is inside of our minds is in some way controlling our reality. What I mean by that? The content of our thoughts are the reality that we are experiencing.
Therefore if we change our thoughts we change our reality! It's simple actually! But someone must actually be willing to try consciously in order to see the effects that our thoughts have on ourselves.
Basically when our thoughts change the perception of our reality changes. For example if I am always thinking that I am gonna fail at the University then thats propably what is gonna happen. But if i change my thoughts and I start thinking that am gonna do great at Univerisity then that is what is going to happen!
Our minds are the ultimate weapons in everything that we want to accomplish. Anything we wish to achieve is possible. But we must change the way of our thinking! Nothing is impossible if we have the will and the mindset! We just have to try!