Where does the point of being disagreeable come from and what purpose does it serve in the business world, in your opinion or according to these books?
You need at least one or two somewhat disagreeable folks in a team. Because without this, groupthink emerges, teams have too much inertia, they follow the assumed norm instead of challenging it for something better, they don’t debate the options enough. That disagreeable energy, in the right dose, leads to better decisions. If you don’t have it naturally, you can encourage someone to “play devil’s advocate” in decision discussions (or do it yourself) and you’ll find sometimes the devil’s advocate is actually right.