In my experience, it's the gap in understanding. To someone with 10+ years experience, certain motes of knowledge might be long-worn givens, where to a beginner

In my experience, it's the gap in understanding. To someone with 10+ years experience, certain motes of knowledge might be long-worn givens, where to a beginner it could be groundbreaking wisdom. Without proper introspection, it can be difficult to correctly identify "What doesn't a beginner in this field know?"