lend someone a hand: help someone.
"I can't do this alone. Can you lend me a hand?"
leave well enough alone: do nothing (because doing something would make
things worse).
"Don't tell Jim how to discipline his children. Leave well enough
alone."
a let-down: a disappointment; something that's very disappointing.
"It must've been quite a let-down not to be chosen for that job.
I know you really hoped you would get it."
Let sleeping dogs lie.: Don't cause problems by doing someth
