Some days work sucks. We start out with good intentions, but our energy levels are low and we go from constructively improving our website to surfing the App Store looking for new games to play.
One response to this kind of procrastination is to force yourself to continue working. You plug away at whatever task you said you would work on at the beginning of the day, but achieve little. This can feel like banging your head against a brick wall and prove remarkably unproductive.