This paper is on the background of so-called KNOW WHY Thinking-a systemic approach that can be used to reflect on all kinds of complex situations. The approach is based on evolutionary logic, according to which everything in the world, whether it is a product, an organization, a project or an individual needs to both adapt and develop in order to be successful. It needs to adapt to its environment and surrounding circumstances: this is referred to as its need for integration. It also needs to develop with the changing environment and in many cases also beat out the competition: this is referred to its need for development. While many systems theories describe how certain systems work, this approach describes why they work and also why other systems do not. This paper provides a range of examples illustrating this. One very useful way of applying this mode of reflection is using it to explain the motivation of human behavior. Humans either act based on rationality and discipline, or they are motivated by feelings. All our feelings can be categorized into two groups: they either help us to integrate into our environment or to develop so that we can adapt to changes or compete with others. No human emotion exists that cannot be categorized into one of these two groups: we follow evolutionary logic. Reflecting on human behavior in this way allows us to understand other-in many cases contradictory-approaches that explain human motivation. Both the KNOW WHY of success (of systems) and the KNOW WHY of human behavior can be used to reflect on our daily challenges. Together with a cause and effect modeling tool, all of the ideas and principles behind KNOW WHY can be applied as the so-called KNOW WHY Method. This method helps you to include the crucial factors within a model. Not only is this approach very powerful-it is easy to use, and therefore has the potential of being applied by many more people than other, rather complicated and abstract systems approaches are.