One of the main problems arising from playing too much your game, is that you, sometimes, loose connection with the level of difficulty of the game. The more you play, the better at it you become, and the simpler the game will look to you. This will create a deapth spiral in the increase of the game difficulty that will result in the game becoming to hard to play and hence, loosing traction toward your potential players.
One of the solutions is, on regular bases, to have some external to the development team playing the game and providing his opinions on the game. Like this, the possibilities to go over the edge with the difficulty level will be somewhat mitigated.