bestofwikipedia:

The Tetris effect occurs when people devote sufficient time and attention to an activity that it begins to overshadow their thoughts, mental images, and dreams. It is named after the video game Tetris.  People who play Tetris for a prolonged amount of time may then find themselves thinking about ways different shapes in the real world can fit together, such as the boxes on a supermarket shelf or the buildings on a street. (via atestu)