Turns out that there’s a strong correlation between a student’s grade and their assessment of the professor’s abilities. Very interesting. I don’t listen too carefully when a poor performer tells me how awful their previous manager was. Wait, what? Are we confusing correlation with causation here? Let's say, for example, that a manager tends to give female employees poor ratings (or whatever BigCo calls a grade). Do…
Interesting data point for you. First, Break All The Rules found that average managers put most of their time into their worst performers. Great ones put most of their time into their star performers. The reason? Both groups can improve, and a 10% improvement in a star is worth a lot more than a 10% improvement in a dud.
I agree with the idea that it's a poor idea to spend most of your time with your worst performers. The problem with the worst employees is that many of them are irredeemable, so you can't get 10% improvement out of them, except possibly by micromanaging them to the point where you're doing their work)--and that doesn't scale. They're unmanageable in a negative sense, and thus you need proportionally more investment to get poorer returns.
One strong exception to a dictum against spending time with worst performers: Spending time identifying unmanageable poor performers does generate very high returns IF YOU FIRE THEM. In software, poor performers can actually have negative productivity: Their presence slows the rest of the team down.