Let alone
Is used to show that if one thing is difficult or impossible, then something else is even more difficult or impossible. It emphasizes that the second thing is much harder than the first.

Examples:
1- When his aunt asked if he liked the sweater she knitted, he said it was beautiful, even though it wasn’t his style, to make her happy.
2- He used a white lie to explain why he was late to meet his friend, saying he got stuck in traffic when he had just been running late.