When Yip Goo Sing first appeared in the LUK SIU FUNG saga, the first thing that both Luk Siu Fung and readers probably noticed was how similar Yip Goo Sing was to Sai Mun Chui Sheut. It was already known that Yip Goo Sing's swordsmanship rivaled or maybe even slightly bettered Sai Mun Chui Sheut's, but it was a surprise to learn that Yip Goo Sing also dressed (all-white) and behaved very similarly to Sai Mun Chui Sheut. Luk Siu Fung even wondered to himself if only this kind of person could attain the highest pinnacles of swordsmanship.
As the story of THE DUEL unfurled itself, we gradually came to see the differences. Sai Mun Chui Sheut, by the time of THE DUEL, had reclaimed some portion of his humanity. He was capable of love (his wife and unborn son), compassion (he spared Aunt 13, who had betrayed and murdered her husband Lee Yim Bak; this was the kind of villain whom Sai Mun Chui Sheut would have killed in cold blood in the first LUK SIU FUNG story arc), and friendship (with Luk Siu Fung). Yip Goo Sing seemed to represent Sai Mun Chui Sheut's "dark side" - what Sai Mun Chui Sheut could have turned into without the leavening influence of family and friends.