The Art of War by Sun Tzu. It might be a bit of a cliche but it really is profound and is actually more useful than I first thought. Especially "show strength

The Art of War by Sun Tzu. It might be a bit of a cliche but it really is profound and is actually more useful than I first thought. Especially "show strength at your weakest, show weakness at your strongest" is something that I've used during negotations and presentations. It sounds like common sense when you read it, because you've seen a lot of this stuff work out ahead of reading it, but it's only once you read it that it becomes abstract and defined enough for me to apply it.