Everything in the past is a prologue.

"What's past is prologue" comes from Shakespeare's play "The Tempest". The original text of this sentence is: What's past is prologue. The meaning of this sentence is: the past is past, what happened in the past will become the prelude to today's events, and we should focus on the present.

"The Tempest" was written in 1611. It tells the story of the Duke of Milan whose title was usurped by his younger brother. He later fled to a desert island with his only daughter Miranda, and relied on magic to become the owner of the island. Finally, Prospero regained his title, forgave his enemies, and returned home.