This idiom comes from an ancient story:
A farmer was working in the field when — thump! — a rabbit ran into a tree stump and died.
The farmer happily brought it home for dinner.
He thought, “Wow, that was easy! I’ll just wait here every day for more rabbits!”
So he stopped farming… and kept staring at the stump.
Of course, no more rabbits came.
His crops died, and he had nothing left.
This became a warning: Don’t count on the same lucky thing happening again.