This is the 6823rd most frequent Russian word.
forgotten
The Russian word for "forgotten" is **забытый**, meaning "no longer remembered or neglected."
Here, 'забытый' (forgotten) functions as a past participle and describes the diary as an object that was forgotten.
Она нашла свой забытый дневник.
She found her forgotten diary.
Here, 'быть забытой' (to be forgotten) employs the past participle in an instrumental feminine form, referring to the story and conveying the sense of not allowing it to reach the state of being forgotten.
Мы не позволим этой истории быть забытой.
We won't let this story be forgotten.
In this sentence, 'забыто' (forgotten) is used as a neuter singular form in the passive, applying to the place as being in a state of being forgotten.