Yes, Success and Fail make a set. All loyals need to play Success into the mission, while minions can choose to play either.
If they were random, a loyalist could get two fail cards and could not play according to the rules of the game. Also, the word set suggests non-random.
Thanks for the fast reply, I just wanted to make sure I hadn't got it wrong
And you're completely right on the assesment, that is why I was wondering, since it also clearly states that a good player must always play a "success" but with random split it could be fairly possibly that the good player would sit with two "fail".
Anyway just wanted to make sure, play commences this weekend.