If a nova reaches naked eye brightness, and nobody sees it, does it exist? Almost certainly.
While visiting AAVSO Headquarters in early February 2013, LSU's Brad Schaefer noted that since the Second World War, there has only been one nova to reach second magnitude, 1975's V1500 Cyg (Nova Cygni 1975). Prior to world war two, there were 1-2 per decade. Is the universe conspiring to have fewer bright novae? Probably not. Brad made several suggestions as to why this might be the case, but it may come down to fundamental changes in how people have observed the sky during the past 50 years. Improvements in observational technology may have enabled the community to find more faint novae, but these may have in turn taken our attention away from events that might've been obvious to our predecessors.
We have a lot of technology at our disposal today, and the science we're able to do with it is expanding exponentially. But regardless of what equipment you have at your disposal, don't forget to look up once in awhile -- you might be surprised by what you see!