The background for this paper is the rapid changes that currently manifests around the globe. The premise is that system science can provide a basis to enhance the capabilities of system engineering to meet these challenges. This paper explores with a few examples how system modelling, decision making and methods to manage complexity can draw on the science. Additionally, it will be explained that humans do not take all decisions on logical bases, hence, the framing of the question allowed by the system model is vital. The result of the paper is a proposal of a framework for knowledge management modelling based on the science and major lessons learned in modelling and methods to manage complexity.