The ABC model, used in cognitive-behavioural modification therapy, has moved out of the psychotherapeutic milieu and is now widely accepted. It provides a scientific argument for the cliché "it's all in the mind". A (activating event) is the event that affects us, B (beliefs) are our thoughts in the situation, C (consequences) are our feelings and behaviour in the situation. The ABC model reminds us that our feelings and behaviour are not directly determined by the situations we encounter, but by our beliefs about them. We interpret the situation in some way and it is this interpretation that will trigger emotions. And the way to control emotions is to change our thoughts.
A -> B -> C
In many situations, it is sufficient to become aware of the thoughts that arise in us in connection with a situation, to examine their reality and, if necessary, to reformulate them in order to calm or eliminate unpleasant emotions. We may find that the method often produces very rapid and effective changes in our mood. This model is very simple and easy to understand. But there is a danger that its very simplicity can make it simplistic and lead us to expect ourselves and each other to achieve rapid healing/change.

Not only do we experience situations in our daily lives in which this psychotherapeutic technique fails us with varying frequency, but the inadequacy of this model has been the subject of scientific research. Different therapeutic trends have tried to nuance and complement the relationship between facts, thoughts and emotions in different ways.
One of these approaches says that the process actually takes place in two stages, described by the following formula:
A -> B -> C
A1 = C -> B1 -> C1
A concrete example may help to illustrate this abstract formula. Let the external situation (A) be that I see a tame stray dog. My thought about the situation (B) is that this dog must be rabid and will bite me. The emotional consequence of this thought (C) is fear. This fear (C) will act as an internal event (A1), an internal activator, in a subsequent process. I think (B1) of this fear that I am a cowardly person who should not be panicked by a stray dog. As a consequence of my thought about the fear (C1), I will feel anger towards myself. (The process can swell into a downward spiral by continuing with another stage where anger towards myself becomes an internal activator, etc.)

According to the original ABC model, my unpleasant emotion (C) is fear, and I can help reduce it by explaining to myself that this dog doesn't look like a rabid dog at all, so I have no reason to fear it. Yet there are times when this thought will make me feel even more uncomfortable. What happens then is that the emotion worth working with is not fear (C), but anger at myself (C1). If I say to myself, "this dog doesn't look rabid at all, so I have no reason to be afraid", it only reinforces the B1 thought that I am a coward. It only makes me angrier at myself.
Mindfulness can help us at point B1 in the process. I can notice my fear (C = A1) and say to myself: "I am scared now. I am allowed to be afraid. I can observe how I feel this fear in my body. At the same time, I know that my fear is not now authentically showing me a way to behave. I can walk past the dog and still very much feel the fear of him." A meaningful attitude changes the B1 thought, and therefore the C1 feeling of anger towards myself no longer has any legitimacy. If I am no longer overwhelmed by anger, I may even be able to see that this stray dog is indeed gentle and friendly, and even if I feel some fear towards it, this fear will not determine my behaviour (e.g. I will not run away).