Do you lose sleep over rules of grammar?
I usually don’t, because I was lucky enough to grow up in a household where both parents insisted that I speak correctly all the time. My father was a writer and, frankly, a snob about English. His mother (who died before I was born) was from Oxford, and he spoke with an English accent his entire life, even though he’d never stepped off North American shores.
We were required to pronounce the word tomato, toe-MAW-toe, or get in trouble. Trust me, there were no ain’ts in our house, no sentences without verbs, and no double negatives.
As a result, I can usually count on my ear to guide me, even when I don’t fully understand the grammar rule.
The one exception? Who versus whom. I always have to think really hard about which word to use, even though the grammar isn’t terribly complicated.
I think my hesitation arises because so many people don’t bother using “whom” at all; they just say “who.” As a result, my ear (and likely yours) has never been exposed to the necessary “training” to make the correct choice.