Questioning yourself is the first instinct of an A player. They don't believe they have all the answers, they believe that they are frauds in a lot of ways because they see the large picture and realize that they cannot hope to know all that is required to be an expert in all areas. Instead they become proficient in understanding the thought-processes that lead to expertise in multiple "specialized" fields and apply it to all areas of endeavor.

Anyone who thinks they are an A player quite frankly isn't.