don't understand how Dan & Blair happened???

lol neither did I :))
but seriously , I guess it was Safran's wild idea to have everyone in the show hook up and I guess they finished other storylines and decided to make them get together , they were friends and I loved this about them with the love/hate relationship, it was perfect, bur then they had to make Dan fall in love with her and this not only hurt Chair's storyline but also Derena's .... I still can't explain :)