It's good to keep your pets' terrarium clean.
John has a goldfish.
John wants his goldfish to live a long time.
John cleans the fish tank diligently and keep track of his goldfish's health.
John never cleans the tank for his goldfish but gets it a lot of toys and talks to it a lot.
John's goldfish lives many years and keeps him company.
John's goldfish gets an infection from the dirty water and dies.