The idiom "necessary evil" refers to an action that is morally wrong or undesirable, but is necessary for achieving a greater good or preventing a worse outcome. It suggests that the action itself is not inherently right, but it is justified by its results.

The idiom "back to the drawing board" means starting over, going back to the beginning of a project or task, or having to reconsider an idea because it didn't work out as planned. It can also imply frustration or disappointment when plans don't go as expected.

The idiom "on edge" means to be extremely tense, anxious, or nervous. It can also indicate that someone is irritable or easily frustrated.

The idiom "fall from grace" means to lose one's status, honor, or position of authority due to a fault or mistake. It can also mean a sudden decline in popularity or favor.

The idiom "go with the flow" means to follow a course of action that is natural or easier, rather than trying to resist it or change it. It can also mean being willing and flexible in adapting to changes and events that are outside one's control.