Proactive condition monitoring, diagnosis and prognosis of modern complex engineering systems are becoming an increasingly challenging issue. This is mainly attributed to the dynamic global scenario and the ever increasing stakeholders conflicting interests. One of the most important missing links that is often given a low priority while assessing the health of a complex dynamic system is the key criticality of the system in question. This paper discusses some of the challenging issues facing the Asset Management personnel and highlights the importance of incorporating criticality aspect of the key performance indicator in the diagnosis and prognosis of all modern complex systems.