You have $100,000 – what’s the best way to use it? Should you spend two years in your entry-level job or undertake postgraduate study? Should your company invest in a new machine or a new factory? How do you go about making the correct decision? How can you test possible solutions in the real world?

In the last two parts of the book, we’ve provided mental tactics that help you gather correct and relevant data as well as understand causal relationships. We are now at a critical juncture, the transition from input (collecting evidence and connecting the dots) to output. This part is all about making decisions, developing solutions and testing them in the real world.

In Chapter 7, we will start with a mental tactic fundamental to rational decision making: thinking on the margin. In Chapter Eight, we will introduce the scoring approach, a framework for making rational decisions. In Chapter Nine, we will look at experimentation as an agile way to test your solution in real life, before rolling it out on a large scale.

Our goal here is to help you take the information you’ve gathered and analysed in the previous two parts of the book and start to take action.