The first three chapters have introduced the ETTO principle and described some forms of this pervasive phenomenon. As these chapters have suggested, there is no shortage of real-life situations where the ETTO principle can be found. Indeed, because it is such a nearly universal characteristic of human performance, it may actually be hard to find an example on either an individual or collective level that does not exemplify it in one way or the other. While this chapter will present further examples from various domains, the main purpose of this book is not to convince anyone that the ETTO principle is real in a philosophical sense. It is rather to consider the consequences, in particular for safety, of this way of describing what humans and organisations do. It is only by having an adequate understanding of the nature of individual and collective performance that we can ever hope to be able to control it. And control is necessary to be safe – or for that matter, to be efficient.