New game development students are often so excited to have the opportunity to make their own games that they fail to see the importance of understanding the tastes of an audience unlike them. I point out to my students that as connoisseurs of games, we developers are unusual- we live and breathe games almost everyday and our perspective is not the same as most players.
In a way, casual players are akin to "muggles" (to borrow the term from a popular series of books about a wizard with glasses and a lightening bolt scar on his forehead.) Non-gamers don't have the same experience with the usual video-game communication conventions and long standing methods that have been built up over decades of gameplay evolution. Many of these long standing communication schemes, while intuitive to gamers, may be enigmatic to many casual players.
Being able to design a game for "muggle" (non-gamers) should be a key part of a designer's toolset. In this article on Zam, designer Zach Gage points out some interesting approaches for over-coming this issue - the use of every-day objects.