There is a big difference between making good parts and developing a good process. The problem with traditional troubleshooting is the focus on making good parts.
Good Parts vs. Good Process: Just because you are making a good part does not necessarily mean you have a good process. If your technicians only focus on making good parts, then they are just concerned with making an acceptable part at the moment. Unfortunately, if there is not a good process making a good part, then the process may not be robust enough to compensate for variability. A good molding process is designed to compensate for the natural variability of plastics.