Certain features of tasks make especially difficult for humans. These constitute leverage points for applying intelligent technologies, but there's a flip side. Designing complex cognitive systems is itself a tough task. Cognitive engineers face the same challenges in designing systems that users confront in working the tasks that the systems are intended to aid. We discuss about these issues. We assume that the cognitive engineers will invoke one or more knowledge shields when they are confronted with evidence that their understanding and planning involves a reductive understanding. The knowledge shield phenomenon suggests that it will take effort to change the reductive mindset that people might bring to design a CCS.