I forget where I first heard this distinction between expertise and experience:
- expertise: theoretical knowledge
- experience: practical knowledge
It's possible to have degrees of one, or both, or to have neither in some area. Apart from its utility as a heuristic for remembering to look to test at different levels, it serves to remind me that the people on any project have different combinations of each and their mental models reflect that.
The manager knows there's a hammer that can be applied to the current problem: just how hard can it be? The implementer knows what to hit, and where, and just how hard it can be.