90% of the time "Managing an underperformer" = you're a bad manager. "Managing an underperformer who thinks they're doing great" = you really suck at managing

90% of the time "Managing an underperformer" = you're a bad manager. "Managing an underperformer who thinks they're doing great" = you really suck at managing but have no idea, and you're missing out on the irony. This is up there with teachers who cant teach and tell their students "50% will fail the class".