The metric isn't "number of completed tasks". That would be a terrible metric. The metric is "amount of valuable work completed", which is a combination of numb

The metric isn't "number of completed tasks". That would be a terrible metric. The metric is "amount of valuable work completed", which is a combination of number of tasks and how much work (and value) each task is. The manager who assigns tasks should have an understanding of the expected amount of work for each task and the expected difficulty.