Definition
This idiom suggests that when something or someone is no longer visible, it is easily forgotten.
After she moved away, we never contacted each other again; it's really a case of out of sight, out of mind.
He always says out of sight, out of mind, which is why he never keeps in touch with his ex-girlfriends.
After I packed away the old clothes, I completely forgot they existed; it's truly out of sight, out of mind.