Negotiation
You need to negotiate with other people. OK, if you're selling a consumer app, you probably don't negotiate with your customers: you set a price and they either pay it or go elsewhere. But that doesn't mean negotiation is limited to people dealing with terrorists and kidnappers. You might want to convince the rest of your team that it's worth rewriting some component, or that a feature you want to build should go into the product. You might want to ask your manager for more responsibility. Perhaps you want a vendor to fix a bug in their software, or a supplier to give you a preferential discount. In any of these cases, you'll need to negotiate. (L looked up the etymology of "negotiate" in the Oxford American Dictionary. Apparently, it comes from the Latin "otium" meaning leisure, so "neg-otium" is "not leisure" or, in other words, business. That's got nothing to do with this book but it's really interesting...