I have been considering baking some bread today. When I first started making bread, I had to follow the recipe very carefully. Each time I made it, I learned something about the qualities of bread and what was essential to making good bread because each time, no matter how hard I tried, some error would creep in -- a mis-measurement, the wrong temperature, too much humidity, something. From the errors I learned what was essential and what was not and how to work with less than perfect conditions. And by repeating the process many times, I learned what makes the difference between a leaden mass of hard dough and a beautifully browned and fragrant loaf of bread. Now that I have made bread many many times, I can be less rigorous about following the recipe. I can add ingredients, change them, make substitutions so long as I stay with the essential elements and requirements of turning flour and liquid and yeast into bread.
Doing therapy is not unlike baking bread. The therapist first needs to learn the recipe and follow it carefully -- that is what new therapists do. And they must do this until they have a solid understanding of what the essential ingredients and conditions are. Therapists need to learn about the frame and why it is essential to the process. And learn what kinds of deviations -- alterations to the recipe -- work and which will likely lead to something less than desirable.