I write in in stunned disbelief, since there are three viewers above me expressing disbelief and even prejudice, at the 'big reveal' in this episode. As this is a spoiler-free comment, I will just say that Flint's motivation and character continue to deepen and much of his determination and almost maniacal drive is explained: he is both running from his past and even from his sense of himself. His reserve and distance makes more sense than ever. The sensitivity shown in how this was done through a series of well-timed flashbacks and real-time action was highly effective.
Black Sails is so much more than a 'pirate show'. Like 'Vikings', which in some ways it closely resembles, it is a study of human nature as much as it is a costume drama. Brilliant TV.