There are some who think their measure of a soldier is how bold and loud he can be, whether or not he's the most skilled or knowledgeable of the group. The braggart or performer can be perceived as being more soldierly because of the attention he draws to himself, with his sometimes bullying ways being seen as attempts at "leadership" among his peers.
The grey man, on the other hand, is usually that soldier who seldom draws attention to himself, either by trying too hard to show his stuff to the staff, or by screwing things up and constantly needing correction. This attribute, by requiring less staff attention than others at either end of the spectrum, causes him to fade into the background if staff are not careful to properly watch for the development of and evaluate skills rather than performance art and failure to perform.
The grey man is often the one accruing the better test scores because he quietly studies, often passes practical tests on the first try because he was paying attention to the lectures, and can usually be found helping his less skilled peers without drawing attention to the fact that he has done so. Being the grey man isn't a bad thing, it's just recognized that the grey man might be missed in some assessment approaches and not necessarily get the recognition he should.
All that being said, some of the best officers and NCOs I have known were the grey men in their training years. They were too busy learning their profession to seek opportunities to show off their knowledge.
