Criticize the behavior, not the person. Key advise in education when it comes to the behavior management of young people or, indeed, the leadership of professional colleagues. To understand why that is essential, rather than simply accept it as axiomatic, we need to refer to the work of Carl Rogers.
Quoted from Simply Psychology.
Carl Rogers (1951) viewed the child as having two basic needs: positive regard from other people and self-worth.
How we think about ourselves, our feelings of self-worth are of fundamental importance both to psychological health and to the likelihood that we can achieve goals and ambitions in life and achieve self-actualization.
Self-worth may be seen as a continuum from very high to very low. For Carl Rogers (1959) a person who has high self-worth, that is, has confidence and positive feelings about him or herself, faces challenges in life, accepts failure and unhappiness at times, and is open with people.
A person with low self-worth may avoid challenges in life, not accept that life can be painful and unhappy at times, and will be defensive and guarded with other people.
Rogers believed feelings of self-worth developed in early childhood and were formed from the interaction of the child with the mother and father. As a child grows older, interactions with significant others will affect feelings of self-worth.
Rogers believed that we need to be regarded positively by others; we need to feel valued, respected, treated with affection and loved. Positive regard is to do with how other people evaluate and judge us in social interaction. Rogers made a distinction between unconditional positive regard and conditional positive regard.
Unconditional positive regard is where parents, significant others (and the humanist therapist) accepts and loves the person for what he or she is. Positive regard is not withdrawn if the person does something wrong or makes a mistake. The consequences of unconditional positive regard are that the person feels free to try things out and make mistakes, even though this may lead to getting it worse at times. People who are able to self-actualize are more likely to have received unconditional positive regard from others, especially their parents in childhood.
Conditional positive regard is where positive regard, praise and approval, depend upon the child, for example, behaving in ways that the parents think correct. Hence the child is not loved for the person he or she is, but on condition that he or she behaves only in ways approved by the parent(s). At the extreme, a person who constantly seeks approval from other people is likely only to have experienced conditional positive regard as a child.
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Note that Rogers did not argue that poor behavior is to be tolerated and accepted, only that the regard that we have for that person remains unconditional in the face of it.