When you find yourself trying to remember a show (or any works) that's on the tip of your tongue but just out of reach, come here - the collective brain of the TVTropes community can probably help. Post all the details you can remember (examples help). If you're looking for a trope, head over to Trope Finder. Have general questions about tropes? Visit Ask The Tropers!
For what it's worth, I have encountered stories along the lines of "wife getting upset about hypothetical future disaster involving hypothetical victims", just not any involving chickens.
The one that comes most strongly to mind begins with a new bride going down to the cellar to fetch something, noticing a precariously placed axe, and collapsing into tears at the thought that one day she will send her yet-unborn son down to the cellar, and the axe will fall on him and kill him.
@Paul A and Mazz:
Yeah, I'm probably thinking of one of the variations. *wry grin* Given my sister-in-law is Russian, it was probably kind of silly for me to try to invoke that kind of cultural shorthand anyhow. Thank you for your efforts.
I had someone point out https://andrewbwatt.com/2009/02/16/the-horse-may-learn-to-talk/
, which is very similar, but with the goal being to teach the horse to talk.

This is kind of an odd niche. I'm looking for a fable or proverb. While at a family dinner, someone was suggesting having family dinners on Sundays once we have kids. My fiancee pointed out that currently our Sundays are consistently booked whereupon her sister-in-law pointed out that our mother-in-law was generally only available Sundays (and that apparently doing such dinners on Sundays was an old family tradition that had been abandoned a decade or so before). I tried to point out that it was silly arguing about dates and availability for something that wasn't happening for years and found myself trying to refer it in the context of teaching the horse to sing (fable where a man condemned to death gets a stay of execution for promising to teach the king's horse to sing, stating to a friend "In a year, I may die. The king may die. The horse may die. Or, the horse may learn to sing.") but I know there's another one more relevant to not arguing over hyptotheticals. I seem to remember it had something to do with a couple planning their life on the farm they will buy and the girl storming off for what would happen to the hypothetical chickens. It's not "Don't count your chickens before they hatch" I'm pretty sure.
Anyone got an idea?