In the Spring and Autumn Period, a farmer in the State of Song was one day working in the fields when he saw a rabbit bump into a tree stump accidentally and break its neck. The farmer took the rabbit home, and cooked himself a delicious meal. That night he thought, 'I needn't work so hard. All I have to do is wait for a rabbit each day by the stump.' So from then on he gave up farming, and simply sat by the stump waiting for rabbits to come and run into it.
This idiom satirizes those who just wait for a stroke of luck, rather than making efforts to obtain what they need.