I don’t think you can teach killer instinct, maybe you can awaken it, but there’s no replacement for the single-minded focus of hurtling towards a goal.
I meet a lot of people who may have some of the requisite skills to be lethal, but very rarely people who have the whole package. I think there’s several reasons for this.
Probably the most important is because while people may often be ruthless and motivated, they may lack the foresight, cognitive power, and force of will to manifest themselves upon the world.
Broadly speaking, seeing the future is something that can be honed, but not taught. One needs to have a grasp of how people work, but rarely will anyone be so direct as to tell apprentices the way of the world, in real time.
Similarly, force of will is something few have. This is because people don’t have the stomach for being disliked, especially when it’s easier to make money by obeying and following. Many intelligent people are risk averse, and resultingly lack the instinct or will to power.
I don’t think people who have a killer instinct are particularly open about having a killer instinct, but it makes sense. Who’s going to come out and say that they’re ruthless?