The first step to addressing any concerns about lackluster work is diagnosing the people issues behind it. Is it a matter of motivation or skill? This doesn’t have to be complicated. You can understand this through a series of conversations with your report. First, discuss whether your expectations are aligned—does “great work” mean the same thing for both of you? Then discuss whether it’s a matter of motivation. If both of those don’t resolve your concerns, then dive in to whether the issue is with skills.