Right!
Now, as I've often posted on these boards, I actually think that Prince Valiant, rather than Pendragon, is Greg Stafford's Arthurian masterpiece. And there are important differences between the two systems when it comes to expectations for how the GM will frame scenes, call for checks etc.
But both systems make it possible for Lancelot to fall for Guinevere even if the player doesn't think this should happen because it would ruin everything. I'm not going to pretend that my Prince Valiant campaign approaches Arthurian levels of pathos; but when Sir Morgath's player, playing the drunk Sir Morgath, proclaimed Lorette of Lothian rather than his wife Elizabeth of York as his true love, it was pretty funny at the table! And sad at the same time, because everyone - including Sir Morgath's player, and probably even Sir Morgath when sober, knew that Lorette had no interest in Morgath. And this was all precipitated by a mechanical framework that allows players to be obliged to accept certain unwanted truths about their PCs.