When Taylor thinks about bringing up her ex, her new date starts talking about the films he watches with his family and she realises 'for the first time what's past is past'.
Why? Because it captures that wonderful feeling of letting someone new into your life when you least expect to. There are far more obvious Taylor Swift breakup song choices ( I Knew You Were Trouble and All Too Well, among others) but Begin Again, the last song on the Red album, is my favourite.