When I was initially exposed to test-driven development's precursor, test-first programming, I immediately sensed the value.
Yet I didn't take the leap, right away. It required a change in my mindset and in my habits. Those things were hard and thus deferred. So years passed with me saying to myself "I really should write the tests for this, first".
What broke me out of the rut was when a test engineer said "I really love your code."