I think that's just a matter of preference on the author's part of which character you are supposed to identify with. Often you are reading the stories from the

I think that's just a matter of preference on the author's part of which character you are supposed to identify with. Often you are reading the stories from the point of view of Watson who also has to attempt to keep up with Holmes as much as the reader does. You are supposed to relate to Watson and keeping some aspects of the mystery hidden is reflected in this. That way the author can make sure the reader has the opportunity to "figure it out" when they feel is best for the dynamic of the story. Jack McDevitt speaks of this concept with his Alex Benedict series of books. The first book is from the perspective of the title character but he changes this to the sidekick for the rest of the series. His reasoning for this, from what I recall, is that it wasn't right for the story to be told from the character's perspective but still have to hide certain things from the reader so that certain ideas don't come to mind before they are ready to be presented. The idea is that if the reader figures out the mystery halfway through the story then the rest of the story to be told is ruined.