Systems theory suggests that every person lives in a system which cannot be considered linear as many different situations causes an effect. Therefore when one person is treated badly, there will be various circumstances that can explain the outcome. The circumstance may be that the person causing the treatment may be feeling bad themselves but need to see it in someone else, which was caused by their own past. It could also be that the person who feels that they are treated badly lacks assertive skills and is not sure how to manage the interaction. Therefore you would have to look at the needs of the system itself (such as system at the workplace or family structure, which is also known as second-order) and the needs of the individual (which is also known as first order) and create a balance.
Using systems theory is also helpful in the workplace, as interactions and behaviour is caused by the system in the workplace. Therefore considering one particular situation may not be as helpful as considering various aspects. As example, suggested by Ms Smith-Acuna, an employee was having trouble with a colleague and felt anxious, unsupported and was too apologetic, however her own way of conducting the meeting (fitting in the with system) needed improvement and she needed to improve her assertive skills (changing the individual) to improve how the meetings functioned, while her colleague needed to change her behaviour as she was critical and impatient. If the change-agent was to only look at the two people, then important details would have been missed. Details of how the meetings were run (system of the organisation) and how the individual fit within the system (second-order system).
Another example is family therapy using systems therapy. A teenager was always angry, but when he was able to manage his anger, another teenager in the family started playing up. It was discovered that the children were expressing the anger that the parent needed to express (of the marriage). However, once the parent realised what was really going on (a system that may have lasted generations and can be resistant to change), the dynamics of the whole family started to change. Systems theory can also help understand that change in behaviour can cause change in systems, however systems need to be considered in two parts - the rules, roles and boundaries that support the system which always works toward maintaining homeostasis and the structure of the system. It is also important to remember that systems also has sub-systems (e.g., department in the workplace) which need to be considered.
In summary, behaviour is often reinforced by the system the person is in as it is providing feedback. You will need to ask is the system causing me to behave, feel or think in this way or do I need to change to fit in the system. What needs to change to create a balance? Often, in the workplace it is usually the latter as some people may fit in the system and some may not and either need to change or move out. You would have to look at the whole picture, and its different parts, to understand the causes.
Source: Systems Theory in Action - Application to individual, couples and family therapy by Shelly Smith-Acuna.
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