Put in a silent room before a blank page, it's almost impossible to write. Neither is it be ideal to work near a television set that keeps drawing one's attention or a room where a child keeps interrupting. In a coffeehouse, its rare for someone to intrude on the space of a patron with an open laptop and a look of concentration. Still, there is just enough conversation and foot traffic in the background that you're forced to semi-consciously tune it out.There's that scene in Butch Cassidy and the Sundance Kid when the latter is asked to demonstrate his shooting prowess, but can't hit the target unless he's moving. On some level, I think the same thing is going on when I write. Forced to focus on a single thing the mind rebels, whereas adding another element somehow focuses it. The coffeehouse somehow provides that element.
Save your eyes. Take breaks.