Why can a process be in control but not be capable of meeting specifications?

A process can be in control if it consistently produces outputs that fall within the predefined control limits, indicating stability and predictability in its performance. However, it may still fail to meet specifications if the target mean or process average is not aligned with the desired specification limits. This situation can arise if the process is systematically offset, producing results that are consistently above or below the specification thresholds. Thus, while the process is stable, it may not be functioning at the required quality level.