How to Memorize

what happens/people are like behind closed doors

Analysis

Something that takes place 'behind closed doors' is something that happens in private without witnesses or spectators. This phrase has a negative or accusatory connotation and implies that what was going on 'behind closed doors' is suspect or underhand or of questionable morals. This can be used in social or professional contexts but is most often used to imply suspicion or generate gossip. 

Social Examples (Advance)

1. They seem like the perfect couple when you meet them in the street, but who knows what they're like together behind closed doors?
2. The people of the town were unhappy that the deliberations over where the council money should be spent were conducted behind closed doors.   

Professional Examples (Advance)

1. Nobody in the office knows what's going on, all the important discussions happen behind closed doors, it's very secretive.
2. Our motto is to praise in public and to give criticism behind closed doors.

Further Suggestions