Possible Clues:

• They should be allowed to be themselves, we're told
• Water under the bridge
• Past things
• Let them be themselves and we'll say no more about it
• Things best let be, proverbially
• Let ....... be .......; don't hold grudge
• Things belonging to the past
• Water under the bridge
• Word after "let" and "be"
• Let these be these to forgive and forget