As a therapist, I am required to follow and utilize methods of treatment that are evidence based. These are methods that have been proven over time to be beneficial to patients seeking mental health services. It sets the stage for "best" practices and if challenged, there is literature, training, and proof to back up what I do. When I was taking classes in school, most of the literature and best practices were based on the works of Freud, Frankl, Skinner, Piaget, Pavlov, Erickson, and Rogers, to name a few. Over the years, other prominent researchers have further expounded or made contributions of their own. The constructs of psychology are changing and evolving as opinion and social norms change and what is considered, "evidence based" is getting harder and harder to define.
As a person who enjoys absolutes, I like to keep my feet rooted in truth and fact. When the truth is bent toward the motivations of another, it's no longer the foundational truth, but a variation of the truth. If you plant an apple seed in the ground and water and tend it, the seed will produce (over time) an apple tree. It does not produce a watermelon. Having said that, there are new fruit and vegetables being produced by manipulation of the original fruit or vegetable being combined or grafted into another. Variations of roses have been "created" by merging two variations of rose to create a third.
When you know the truth about who you are, what you believe, and it is supported by evidence, you can live with confidence. Truth never changes to become a lie. A lie cannot be a lie and remain the truth. The truth is one of those absolutes that does not evolve. Opinion evolves and interpretation of the original truth may change, but the truth is, the truth is the truth.