I didn't say that it was the only part of the job, just that it was the most important thing. Hopefully you have some knobs you can turn. At my current company if people can't deliver you try to hook them up with more mentors and if they still can't deliver, you stop giving them direct labor to work on and eventual force them out because they don't have any work and they stop getting pay raises (or you fire them usually they push them out).