Can you ever know enough about people?
I recently finished 100 Things Every Designer Needs to Know About People.
Susan Weinschenk has compiled a lot of research into a hundred short essays. The book covers a lot of ground with topics ranging from perception, over how human memory and thinking and decision making processes work to how humans tend to deal with errors.
The book doesn't require any prior knowledge. It is very digestible and actionable. The chapters are to the point and contain a condensed list of key takeaways. No reading order is required. Being very broad in topics makes it rather hard to summarize - yet cheapskates and people in a hurry could probably even get some insights out of simply reading once through the table of contents.
All in all: a recommended reading.