Beliefs are meanings about ourselves, other people, and the world we have come to trust and rely on. We develop these deep beliefs out of what has happened to us, what we have been told to believe, and from watching what happens around us.
Children often believe what they are told: “strangers are dangerous,” “Listen to and respect grown-ups.” “Don’t burden other people with your problems,” “You’re bad.”

If you witnessed violence in your home growing up, you may believe that caring people hurt each other, or you never leave a relationship no matter how damaging it might be. On the other hand, your past experiences may have led you to believe you are always safe, that you are in control of what happens to you, that others are always trustworthy, or no matter what happens, things will work out okay in the end.
Because beliefs are meanings, they are based on evidence, past facts, and experience. They are the lessons we draw on to help us know how best to act or react in the present. Once we have formed our core beliefs, we usually stop thinking much about them. They become a natural part of who we are and how we function. We tend to act on them automatically, as reflex.

Beliefs can and do Change 

Most of the time they change gradually as the weight of our experience shapes what we believe. The process is similar to the way a river gradually shifts its course as the surrounding terrain erodes. This process of belief change is called accommodation. It is possible to exert some control and influence over the process. With trauma, however, basic beliefs can change quickly and dramatically. A belief may intensify, become absolute, reverse itself, or collapse altogether.
Survivors of trauma often think in black-or-white — all-or-nothing terms. Overwhelmed with powerful feelings, they tend to feel completely safe or completely in danger, completely in control or completely out of control. This kind of thinking can occur as a reaction to trauma. When trauma shatters a basic belief it can seem best to believe the extreme opposite. It may feel most self-protective not to expect anything positive from yourself or others. If you thought you were safe and suddenly found yourself in a life-threatening situation, it may seem safer always to assume high risk rather than to assume safety. You may then feel better prepared to protect or defend yourself.
Trauma throws you for a loop because it changes your core beliefs about one or more of the five basic human needs: safety, trust, control, self-esteem, and intimacy. We need some minimum amount of each of these things for ourselves and for those close to us. When we don’t get enough of what we need, we can begin to experience distress.
If you are experiencing troubling post trauma reactions, it can probably be traced to a change in your thinking about one or more of these five needs. You may no longer feel safe or able to trust. You may feel out of control, worthless, or alone. You may have any or all of these reactions. If you do, your trauma experience has probably disrupted your beliefs about that need. What did that need mean to you before the trauma? How has it changed since the trauma? What lessons about that need did you draw from the trauma? Are there other possible meanings to events in your current life? Perhaps you do not need to feel hopeless about regaining a sense of safety, trust, or intimacy?

Basic needs often Disrupted by Trauma: 

Safety for yourself: The need to feel you are reasonable protected from harm inflicted by yourself, by others, or by the environment. Safety for others: The need to feel that people you value are reasonable protected from harm inflicted by yourself, by others, or the environment.
Trust in yourself: The need to rely on your own judgment. Trust in others: The need to rely on others.
Control of yourself: The need to feel in charge of your own actions. Control with others: The need to have some influence or impact on others.
Esteem for yourself: The need to value what you feel, think, and believe. Esteem for others: The need to value others
Intimacy with yourself: The need to know and accept your own feelings and thoughts. Intimacy with others: The need to be known and accepted by others.

Actual experience by itself isn’t always enough, we constantly filter or ignore experiences in our day-to-day lives. If you don’t not have an open mind, you will find it difficult to notice evidence when you see it. It is easy to dismiss, ignore, or explain away contradictory evidence automatically. This is natural, but not necessarily in your best interest. It is, of course, wise not to make big changes on the basis of a single experience. However, explaining away experiences as “exceptions” can happen so fast you may not notice what has actually happened.