When released for the first time, a single usually suppose to have a hit on the A-side, and a secondary song not supposed to be a hit, on the B-side. That song was basically used to fill the B-side, and producers didn't give hight hopes on it.
The scope of my question doesn't include singles that knowingly featured two hits (sometimes called double A-side) like The Beatles' We Can Work It Out / Day Tripper or where the letter A or B doesn't appear on the label.
I'm focussing in singles where the B-side became a massive hit, and A-side almost forgotten.
Has a B-side unexpectedly overtake a A-side, in terms of success, popularity?