This past winter, my furnace failed catastrophically. (The furnace repair person told me that when furnaces fail, it tends to be catastrophic failure.) It was a few days before everything was back in order, and the very day everything was working again, the furnace belonging to one of my relatives stopped working.
This was an application of the First Law of Thermodynamics with which I had previously been unfamiliar.
Fortunately, the repair on the second furnace was very simple and was done in just a few hours.
After I informed my friends of my discovery of this law of the universe, one of them wrote, "Our furnace broke on Sunday. I can't help but feel like you're kind of responsible."