Most of C.N. Chan's traits are the real-life traits of Jackie Chan, including his training routines and choice of clothing.
The film was originally conceived purely as a love story, with Chan as producer, but not as one of the cast. In order to secure actress Shu Qi, the script was re-written, and a role for Chan was created. This soon developed into a starring role, and elements of action crept in.
Director Vincent Kok had wanted to use Jackie Chan's office as the set for C.N.'s apartment, but this proved to be impractical, particularly as that section of the office is on the third floor. However, many props from Chan's office were used, including his own training dummy. Chan said of his character, C.N., that he was "sixty to seventy percent Jackie Chan". The clothing the character wears, the training routine he undergoes, and healthy lifestyle he maintains, his general good nature, and his environmental role are all traits and actions of Jackie.
The second time Tony Leung Chiu-wai plays the gay character. The first time was in Wong Kar-Wai's Happy Together (1997).