In Le Morte D'Arthur, Arthur's knights often arrive in mysterious castles only to find that the "custom of the castle" requires them to do something ridiculously difficult, or sometimes just plain ridiculous, like having to fight the castle's lord or even having to allow a lady to be bled. If the knight succeeded in whatever challenge was thrown at him, it provided him with an opportunity to end these barbaric practices, which is yet another way in which he can uphold his oath to promote justice and fairness wherever he goes. Often, the castle's community is just plain relieved to see the custom come to an end, which just goes to show that traditions can sometimes be a burden. But of course customs aren't always burdens. In Camelot, traditions like chivalry, holidays, and religious customs help bring stability to a violent, changing place.
Arthur's knights fulfill their obligation to promote justice and fairness wherever they go by ending barbaric "customs of the castle." This is an example of chivalry taking the place of older, more outdated customs.
Family traditions are the most important codes of behavior in determining characters' behavior in Le Morte D'Arthur.