The premise of Daniel Kahneman’s book Thinking, Fast and Slow is that we employ two very different ways of thinking. The book is very dense, and a highly recommended read. Kahneman says that the main goal of his book is to arm people with a better vocabulary about thinking, which in turn allows them to understand our biases, decisions and behavior better. While that is great for everyone, I think it’s especially valuable for designers. It lets you see that most of the time, there is no ‘one’ user, but one with multiple modes of thinking. Most good designers have observed their users interacting with their products multiple times. Insights from this book let you put more weight on these observations.