I am going to assume that you are asking about The Knight's Tale from Geoffrey Chaucer's Canterbury Tales. The Knight's Tale focuses on something called courtly love. I suppose anybody could do this kind of love, but it is mainly descriptive of how a knight would love his one true lady love. It is loyalty and devotion to the extreme and might even border on worship. In The Knight's Tale and with courtly love in general, the woman is put on a pedestal (metaphorically) and is beautiful and right and perfect in every way possible. There are rules to follow for courtly love, which makes sense for this time period. Chivalry is big and that had lots of rules for how a knight was to honor his king and poor and just about everything, so having rules for knightly love is par for the course. By following the rules of knightly love, a person can become stronger and more honorable through that love.
The problem with The Knights Tale is the conflict between the rules of courtly love and chivalry when two knights (brothers) both fall in courtly love with the same woman.