Le Morte D'Arthur
How we cite our quotes:
So whan the shylde was com, Sir Gawain toke of the case; and whan he byhylde that shylde he knew hyt anone that hit was Sir Launcelottis shylde and his owne armys [...]"So God me spede," seyde Sir Gawain, "fayre damesell, ye have ryght, for and he be youre love, ye love the most honorabelyst knyght of the worlde, and the man of moste worship." (607.8-10, 18-20)
Gawain is surprised to find that the knight who has worn this damsel's sleeve is Launcelot; it doesn't really jive with Launcelot's loyalty to Gwenyvere. But this moment reminds us of another place in the story where an armor-switch caused some confusion -- the "Tale of Balyn and Balan." But how do these two moments compare?
Than Quene Gwenyvere sent for Sir Launcelot and seyd thus: "I warne you that ye ryde no more in no justis, nor turnementis but that youre kynnesmen may know you, and at thys justis that shall be ye shall have of me a slyeve of golde." (618.28-31)
Oh man, Gwenyvere is not happy. That'll teach Launcelot to wear another woman's favor in a joust. Of course if Launcelot wears Gwenyvere's favor, that runs the risk of revealing the one big part of his identity that he's managed to keep a secret so far: his love for Gwenyvere. But maybe that's just it. Maybe Gwenyvere has had it with all this sneaking around, and she wants Launcelot to claim his true identity as her true love, no matter the risks.
"And as Jesu be my helpe, and be my knyghthode, I slewe never Sir Gareth nother hys brother be my wyllynge – but alas that ever they were unarmed that unhappy day!" (668.21-23)
Gareth and Gaheris' lack of identifying armor in battle leads Launcelot to kill them by mistake. Now that's a big oops. The mistake is particularly tragic because Gareth was such a bit Launcelot fan that he insisted that Launcelot be the one to knight him – the very act that, in the long run, put Gareth in this position.