Videosift: Guy takes a photograph of the Stanley Cup with lens cap on

This is a mistake that can be easier to make when you have a rangefinder and having one of the most expensive ones -- a Leica M6 -- doesn't make it any harder or easier to make it.

With a rangefinder you are not looking through the image-taking lens to see if you have something in focus. You are looking through a viewfinder that is separate from the lens. So if you have something blocking the actual image-taking lens, you wouldn't know -- unless you checked ;).