So there’s a story about a guy with a squeaky floor. He tries everything but it won’t stop squeaking. So he hires a contractor to take a look. The contractor arrives, walks around, listens to the squeaks, then pulls his hammer and whacks one nail. Subsequently the squeaking stops.
He bills the guy $500 and the guy complains. Why $500? You hammered one nail? The contractor smiles. That was $1 for the hammering, $499 for knowing which nail.
A good Trainer, inn essence, finds the nail.