Wing Chun, or any martial art, is not magic. All martial arts are based on science. More specifically, the physics of leverage and force.
No martial art employs a physical law uniquely. That is to say, there is no martial art that uses some rule of leverage and force that no other martial art uses. However, how these concepts are passed down is radically different.
Some martial art teachings rely on the simple repetition of a technique. The science governing its effectiveness is essentially buried, and may not be fully understood by some practitioners. As long as the technique is executed properly, the maximum force will be applied to the appropriate lever, and the technique will be effective.
Over time, Wing Chun teachings have tried to uncover the underlying physics, and this is precisely why I enjoy Wing Chun. Certainly, we must attempt to gain an ideal position, which maximizes the effectiveness of the force. However, most Wing Chun instruction, at least to my experience, attempts to analyze the force and leverage and define it in the teaching. The Center Line and Central Line theories are the prime examples of this. All arts employ these ideas, but not many actually define them.
With an understand of how the underlying mechanism works, it is easy to flow outside of the techniques, easier to improvise. It is only then that any martial art becomes your own.