A lot of comments have been made about the gimmick of Andy Lau's body suit but I think the director intentionally used it. Much of the film is metaphorical and symbolic. The movie artfully provides a story that is richer for its indirectness. Just as Daai Chek Liu fights the form of his would be self, and prevents the triggering of a new karmic thread through a potential revenge/ justifiable killing of Sun Ko, the body suit may in fact symbolize the effort that many people put into developing the unimportant/ ineffectual aspects of their lives. In the first part of the movie, none of his highly developed skills or extrasensory perception can avert the eventual course of karma; and only in the second part, when he forgives Sun Ko, is he successful in making any difference.
His shedding of his over-developed physique during this journey is perhaps symbolic of his return to simply pursuing "the only thing that Buddha taught" (per his soliloquy after he resolves the conflict with his alter ego). If you watch carefully, everything you need to understand the story is right there; but it's not obvious. There are many places where the director has only sown the seed for further inquiry. I could go on; but suffice to say it's not a movie that can be fully appreciated without at least some analysis on the part of the audience :) In the end, if your interpretation even makes you think about the laws of nature, the meaning and purpose of your life, that's what matters, and is perhaps what the director/ scriptwriter intended.
