"Ordinarily if an actor gets chosen for the lead in a film, he or she has already built up a repertoire, and everyone knows what he or she is capable of"

This quote by Zhang Ziyi talks to the value of a star's reputation and experience when it happens chosen for a lead function in a film. It suggests that actors who have actually already developed a repertoire of work and have established themselves in the industry are more likely to be chosen for lead functions. This is since the filmmakers already know what the star is capable of and can rely on that they will be able to provide a piece de resistance. It also implies that actors who are just starting in the market may have to work harder to prove themselves and build up a collection of work before they can be thought about for lead functions. Eventually, this quote highlights the importance of an actor's experience and credibility when it becomes selected for a lead role in a film.