"Grandpa is a man with sisu."
Translation:Vaari on sisukas mies.
There's several words for a granpa in Finnish and it depends on he families and what they prefer using. "Isoisä" is the official word, like "grandfather", and I think they chose something else here because of the word "Grandpa". Here's some of the other more common ones: vaari, ukki, ukko and pappa.