Not for everyone, but those who it is for very much should read this - but not without understanding that it can be quite triggering at times. :
The Body Keeps the Score: Brain, Mind, and Body in the Healing of Trauma
-Bessel van der Kolk
It's not an easy read for said people, but very worthwhile. Was introduced at a friends place and got a little ways in, waiting to pick up my own copy now.
Edit:
Also "The Art of War" is fun. It mostly boils down to common sense, but it's interesting to see application of first principles to ancient warfare.
Edit:
Also "The Art of War" is fun. It mostly boils down to common sense, but it's interesting to see application of first principles to ancient warfare.