For the Japanese, moss is something to be admired. Associated with beauty, moss grows on rocks and in pathways of old temples in places like Kyoto. Yet the stone that continues to tumble will never have moss. So this expression is often used to admonish others to stay put, to continue on in the same job. Ironically, this expression is also used by some Japanese to mean the very opposite, i.e., the meaning understood by Americans: keep moving or you’ll get old.
Ichido nyuusha shitara, shooshoo taihenna koto ga atte mo, zutto sono kaisha ni tsutometa hoo ga ii. “Korogaru ishi ni koke musazu” to iwareru yooni shokuba o amari kawaru no wa konomashii koto dewa nai.
Once a person is employed, he or she is better off staying in the same company even when facing hardships. As the proverb “A stone that rolls gathers no moss” goes, it is not advisable to job-hop.