I think it is true when they say narcissists are levelheaded not until you say something that's logical or reasonable.
There's plenty of information available about NPD; but I haven't yet read that they are regarded as being 'level-headed.'
If being confident is being narcissistic than I'd say it does make good traders or in the very least it's way better than not being confident. Some of the most successful poker players seem to have a high value in their self.
Like many things in trading, there is a sweet spot in the middle. Enough ego to be confident that you can succeed is required to become a good trader. Too much, and you cannot admit your mistakes (your mistakes are the main thing you learn from). Narcissists can succeed by hiring the right people. Here is their modus operandi: hire an expert who knows how to do what the narcissist does not know, get it done, then the narcissist takes credit for it. The expert may not even care about getting the accolades if he is well compensated by the narcissist. A really smart expert will even try to make the narcissist think everything was truly his idea. Then the expert will get a bonus. Win-win. Hey, maybe this little anecdote is a good diagnostic tool! Have you witnessed such a scenario at some point in your life? If not, maybe YOU are the narcissist.
I'm not sure I agree. Being confident doesn't necessarily equate to being a narcissist, nor does it equate to having an ego. And I'm relatively young but from the books that I've read and the self help books I've read, they say that the good business owner will give credit to the subordinates when due. Subordinates have a tendency to value credit more than compensation in terms of corporate satisfaction and morale. I don't know if this is 100% true as I'm not a business owner and haven't put this into practice, but it's what I've read.