You walk a narrow line with this question. If you believe a truck is not humming down the highway, while the person next to you, and the driver of the truck, believe that one is, whenever you step into the road in front of the truck you will likely get hurt very badly.
However, not all of the environment is as obvious as a truck. In the sense that many factors, both cosmological and scientific, are not as obvious as a truck, belief in these factors may, in many instances, affect your response to your environment, thus changing the reality of the environment for you. This change may well not include others who are not convinced.
In either case, the environment is not changed by your belief, but your response and interaction with the environment is influenced by your belief, creating the impression that your belief has altered the environment.
I once became so convinced that the Peter Pan thing about flying simply by being convinced, with the addition of a little fairy dust, would allow a person to fly. I have had super-real dreams of doing just that. Levitation! In the back of my mind, I still am convinced of this obvious fiction....if it moved to the front of my mind, would I be able to fly? Probably not.
Belief in your lucky charm probably helps you judge events as being lucky. It does not actually have any effect on them.