"So, I hear you care about rationality. What's that about?"

Rationality is about improving your thinking so that you make better decisions. You know, sometimes you make decisions that turn out bad because there is some piece of knowledge or information that you really needed to know but didn't. But sometimes it turns out even with the same information you can make a better choice if you think about things differently. In the narrow sense rationality is getting your brain to make the best use of the information you have to make the best choice. In the wider sense rationality is about filling your brain up with the best information in the first place.

That might just sound like common sense - that people should think carefully about things - but it turns out that there are a whole lot of really common mistakes that people don't realize that they are making, and it really is possible to learn better patterns of thinking that let you make better decisions.