A childhood belief about family

I used to think that everyone's grandma had the same last name, like your dad's mom had this name and my friends grandma had the exact same name. So i went up, asked my best freind how his grandma (with my last name) was doing..he said he didnt have one. I told him how sad i was. He told me he had a grandma (his last name) i never made the connection of names....i just assumed she was a different age, hence my great-grandma having a different last name then all my others.