We were taught keeping your word is a moral thing — "be a good person." That's true, but it's the smallest layer. Underneath, it's structural. Your nervous system is listening every time you make a promise, and it's watching to see if you'll keep it. That evidence becomes the story you carry about who you are.
Break enough of the small ones — the alarm at 5:30, the water, the walk, the call, the book you said you'd finish — and a quiet verdict settles in: "I can't count on me." Every big goal after that is built on that sand. This is why most people don't fail from a lack of talent. They fail from a lack of self-trust.