At some point, "I've always struggled to follow through" or "I'm just not someone who finishes things" stopped being an observation and became part of how you describe yourself. Once that happens, staying stuck stops being a problem to solve and starts being consistent with who you've decided you are — which your brain will quietly defend, because it's wired to keep your self-concept intact even when the self-concept isn't serving you.
Here's the part worth being precise about. That story isn't sitting separately from your subconscious patterns — it IS your belief system, repeated so often it stopped looking like a belief and became what the course calls your Concept of Self. The 96% Principle, the belief system, the Concept of Self: one mechanism, not three things to untangle.
This is what we mean by Identification with the Narrative — and it's worth naming directly, because nobody can out-effort a story they don't know they're inside of. All long-lasting change happens at the identity level, not the effort sitting on top of it, which is exactly why trying harder at the same approach kept not working.