Once you get the questions right, the answer is often obvious.
In spite of my malaise I needed to repair the iron horse. Our grass, cut maybe 4 times a season, needed to be cut before we left for Boston and it's worse now, only the mower is not working well.
The iron horse is dependent upon a belt to drive the blades, and the belt kept falling off. Replacing it isn't difficult, merely time consuming, and since I had to go to the trouble of installing I chose to replace the belt with a new one. Half a dozen installs, reinstalls, coupled with rough words later, I referred to the teachings of one of the brightest men I ever worked for.
An engineer by trade, he taught all the youngsters working for him to do 3 things whenever effecting a repair. 1. Observe first second and third before picking up any tool or making any decision. 2. Do what doctors do, first do no harm. Make certain you don't break one thing while repairing another. 3. Solve the problem not the symptom.
That advice has become second nature to me except for when I KNOW what's wrong. (reread the third para) So today I sat in my observing chair, simply staring at the mower deck.
I visualized its operation. I compared one side to the other looking for differences. There it was staring back at me all along.
Why was the top of one pulley shiny and the other not? Somehow it worked lose, spinning freely until it became out of round. A few dollars and half an hour later all was well, until next time, and another lesson reinforced and probably soon forgotten.