Feedback is one of the major concepts in systems thinking. Instead of thinking in a linear way, it recognises that as well as one cause (A) leading to an effect (B), B will also affect A in various ways. This circular causality is called a 'feedback loop'. Many elements interacting and coupled in this way result in a complex system, of mutual causes and effects, especially when they involve human ideas, beliefs, minds and culture.
There are two forms of feedback effect - "positive" and "negative" - not in the sense of being 'good' or 'bad', but producing 'self-reinforcing', and 'self-correcting' effects respectively.
Negative feedback happens when an increase in one thing leads to a decrease in another, so bringing the system back into line with its purpose.
Cyberneticist Norbert Wiener used the simple example of steering a boat to illustrate feedback. (Incidentally, the word, 'cybernetics' originates in a Greek word meaning 'to steer'). When the boat deviates to the left, the person steering checks the deviation and moves the rudder to the left to move the boat back on course. Once corrected, the boat may then move too far to the right so that the person steering re-checks, moves the rudder to the left and corrects the position again. And so on. Boats are kept on course by these negative feedback dynamics.
The same basic dynamic can also be seen when a person is anxious or under stress. Pressure in life translates into experience of stress which, in turn, has physiological effects on their body chemistry (adrenal hormones are produced, for example). Something then needs to be done to reduce stress and the production of adrenalin.
Positive feedback occurs when an increase in one thing leads to an increase in another and so on in a domino, vicious circle or spiral effect. In the boat example, when a person steering is distracted, and takes their eye off the horizon or instruments, they will hold the rudder to the left for longer than normal and move the boat off course. The longer this lasts, the further off course it will go until it would eventually turn 180 degrees or more.
The more off course the boat becomes, the more (negative feedback) countersteering will be required to correct it, but also the greater the possibility of 'over-correcting' and veering off course in the other direction.
If levels of stress are not corrected, the body continues to produce adrenal hormones which further contribute to feelings of stress and send the body-mind system into a vicious, mutually reinforcing cycle. Extreme and prolonged stress can result in stress-related diseases, such as cancers, heart disease and depression, excessive habits such as smoking, drinking or eating, and/or increasing difficulty in coping with work and other areas of life.
Similarly, the greater the deviation from a healthy, less stressed frame of mind, the more difficult it becomes to correct it (through drugs, relaxation, change in lifestyle, etc). The danger of overcompensating in the other direction also increases through, for example, dependence on anti-depressant drugs or rash changes in other areas of life.