I get what you are saying. I am guessing mechanics have general theories and guidelines that remain constant while they tinker with this and that to figure out how to solve a mechanical problem. Ultimately, if you take a nuanced look at any problem-solving dynamic, there is often an element of trial and error. Problems easily solved with black and white certainty don’t remain problems for but a short time.
I believe psychologists are working with general theories and guidelines like mechanics do, the difference being that I believe psychological theories misdirect a therapist’s or researcher’s efforts and perpetuate human problems or make them worse. At best, psychological theories help people cope with their discomfort.
I believe we can develop biological theories, and even if they offer guidelines without black and white certainty, they will still do much, much more good for people than existing psychological theories.
Your point is well taken because it helps me adds more nuance to what I am driving at.