To understand how you think, you need to understand how you influence your own reality. We all filter the world through our belief systems. These are unique to each person, although people from the same culture tend to have shared belief systems. The purpose of a belief system is to choose what to pay attention to, and therefore to know what not to pay attention to, without examining it first.
Our belief systems are the result of our environment, but they also to a large extent determine how we experience our environment. In a way, we actually create the world we live in, we create our reality, by first choosing what we want to notice, and then by assigning meaning to what we notice.
The purpose of therapy is to enable the client to make changes in their behaviour. Understanding how belief systems are created and how they influence behaviour is a key aspect of hypnotherapy.
Whether you are happy or unhappy, successful or unsuccessful, is very largely an outcome of your thinking style, of your cognitive filtering, the process use to understand the world you find yourself in. Changing your belief systems effectively changes who you are. Cognitive filtering can be discovered by listening to what a person says, and the mechanisms of cognitive filtering can be used in hypnotic suggestion to target the processes which are preventing change. Cognitive filtering is the basis of Narrative Therapy.
The function of our brain is actually to forget things so as to not clutter up our awareness with stuff that is not important. You were not aware of the temperature of your left foot until you read this sentence, were you?
We are flooded with sensory information from our environment and from within our own mind. The mind has to consider this information, decide if it is immediately useful, and if not, to delete it. For a simple demonstration of the deletion effect, just close you eyes now, and try to recall five colours of things that you would see when your eyes were open. Most people get the colours hopelessly wrong when they try this. The objects and their colours are not important to survival so they are not monitored. This means that effectively, they are invisible - your mind deletes them.
The deletion occurs instantly and without conscious awareness. Unfortunately, if the mind believes something is true, and does not want to have that belief challenged, then any incoming information which does not fit that belief gets deleted. It is just discarded and never gets processed.
A woman can fall in love and live with a man who is inconsiderate and selfish, but since this is incompatible with with her belief that this man was destined to be her soul mate, his behaviour gets deleted. It just does not register: she doesn't just put up with it, she actually doesn't notice it all. It is only when he finally gets too much that her mind allows the behaviour to be noticed. She finally sees what all her friends have been telling her since the beginning.
It is possible to use this facility in therapy by suggesting to the client that they can choose to delete and ignore things that are bothering them.
The brain has a tendency to expect any new information to match its existing beliefs. If the new information matches the beliefs then the information is processed normally. However, if the new information does not agree with the existing beliefs then it is either ignored (deleted) or it is distorted to fit the belief.
In therapy, a situation can be re-examined and restated so as to make it fit with the client's current beliefs. This is the basis of reframing.
Putting things into categories is a fundament human trait. We tend to examine a thing once, decide that it goes into some particular category and then never really think about it again. Every time we encounter that thing again, we look to the category for information, and behave by reacting to the category, rather than the thing itself. This saves a lot of time and mental processing but frequently leads to faulty thinking.
The problem is that once we have decided something belongs to a particular category it takes on all the aspects of that category and is always treated as being of that category. Even if it is in the wrong category. For example, some people will say that they don't like classical music. The moment they hear something that sounds like classical music they mentally turn off, and tell themselves they just don't like it, without really listening to it. They classify all classical music as 'something I don't like'. And because they never really listen to it, it never gets a chance to be re-classified. The same applies to other categories like 'curly-haired men', or 'people who annoy me'.
Once a thing/person/idea has been sorted into a particular category it is very difficult to move it out of that category. This is because we never really look at it again properly. Before we can reclassify it, we have to notice it. A thing already classified has to be astonishingly different before it is different enough to be re-examined. If you see a man every day and he is gradually losing his hair, the realization that he is nearly bald comes as a surprise one day. On the other hand, if the same man walks in one day and has shaved his head completely bald, you would notice immediately.
This is known as the Threshold Effect. You do not notice a change until it exceeds some sort of threshold.
In therapy, in order to get people to change how they think about something, that something has to first be noticed. Teaching the client to become aware of small differences will allow the client to discriminate between situations so that it can be reframed as something else. When wording hypnotic suggestions the discrimination threshold can be used to make clients notice small changes and then to suggest that noticing these small changes means that the therapy is working, and that this small change is proof that a large change is happening.
The human mind learns by association. When coming across something new and unknown the mind tries to match it with something already known. The various elements that make up the new thing are compared to known elements and when sufficient elements are matched the new thing is accepted as being essentially the same as known thing. This prevents excessive time and mental effort being expended on minutely examining each new thing we encounter before deciding whether it is dangerous or not.
Imagine how long it might take if every different species of bird had to be examined in detail before accepting it as a bird. Instead we mentally construct a set of rules for distinguishing 'bird-things' from 'fish-things'. There are fish that fly and birds that swim but our brains are superb at creating rules to classify similar things and exclude things which differ in some significant detail. These rules are created automatically from only a few examples. A child does not need to see hundreds of different birds in order to come up with rules for what is a bird.
Unfortunately our brains apply the same rule-generating process to everything and in the search for speed our brain often exclude examples that should be included or includes things that are in fact different. Over-generalisation can be a major problem, for example, a woman who grew up in a dysfunctional household may form the belief that 'all men are violent' and behave as if this was always true. Inappropriate generalisations are at the core of many behavioural problems.