For this year, mine was Thinking Fast and Slow by Daniel Kahneman.

TL;DR - the book explains how humans are predictably irrational and how seeming cognitive ease in decisioning is simply laziness in action since the brain will substitute a tough decision for a similar but easy one! It has made me reflect upon why I think the way I do, helped me to remove most bias from my actions, and also has a great suggestion that you should ask others to check you if you sound stupid, which is not great for your ego but is necessary nonetheless.