Ever been so convinced you're right that you'll ignore the obvious solution staring you in the face? I once tore apart an entire fuel system on a hunch, swearing it was the pump. Plugged in the scanner as a last resort and found a single faulty sensor. Felt like a proper fool, but hey, at least I got a workout. Now I joke that my scanner is my best mechanic, and I'm just the guy who turns the wrenches. Stubbornness might be free, but it sure ain't cheap when you're buying your own time back.