I broke the house.
It takes a real talent to screw up such a simple task. The shower faucet was leaking. I shut the water off to the house, removed the faucet cartridge, and proceeded to the hardware store to get a replacement. No luck. I went to Home Depot, and showed a guy what I was looking for, and he said "I can almost guarantee that we don't have one of those" but he took me to where the faucet repair items were in an attempt to look. He didn't find one that matched mine, but suggested the washer on the end might be the problem, and he removed a screw from the cartridge, removed the worn washer, found a suitable replacement washer, and affixed it with a new screw. The washer was sold in a package of 10 that cost me $1.47. He didn't charge me for the screw. I returned home, confident that the repair would soon be complete. I replaced the cartridge. Turned on the water to the house, and lo and behold, the leak has ceased. (Hooray!). However, the water pressure never made it back up to where it was before. The water at the kitchen sink trickles out. The toilets, once flushed, struggle to refill their tanks. I can't imagine what I did that would affect the water pressure to the whole house, but leave it to me to screw up such a simple repair.