Different kinds of knowing
Conceptual understanding, emotional expectation, habit, bodily response, and relational learning overlap, but they don't always change together. You can update one, say, what you consciously believe, while the others continue operating on older information.
This is why "I know that, but..." is such a common sentence in therapy. It isn't a contradiction. It's an accurate report of two different systems that haven't yet agreed with each other.
When change actually happens
Change of this kind tends to happen less through repetition of the correct idea and more through direct experience that genuinely contradicts the old expectation while that expectation is active. When an old pattern and a new, believable reality show up at the same time, something in the system has to reorganize, because both can no longer fully describe what's happening.
That's different from positive thinking or willpower. The contradiction has to be real and grounded in your actual experience, not simply asserted. When it lands, the old reaction can be seen clearly as something that just isn't relevant anymore.