What figure of speech is "You are a thorn in my side."

Idiom.

Explanation:

Idiom is a fixed expression that has a figurative meaning different from its literal meaning.

Challenging times can often bring out both the best and worst in people.

Explanation:

In "The Diary of Anne Frank", the theme that peace is often not appreciated until it has been lost is represented in the part when Anne and the people that were hidden, without much hope of being alive the next day, with the uncertainty of whether or not they would be discovered at any time.