I think procrastination is the bane of most authors.  Having carved out time to write, cleared the calendar, it is all too easy to lose a couple hours on social media or “just one more turn”-ing it through a computer game.
Apparently there’s a study out that shows this may not be “You’re a bad time manager…” but actually “Something is emotionally bothering you.”  I’m certainly willing to entertain the argument–I know that emotional upheaval can be a double-edged sword as far was writing motivation goes.  (“Double edged?”  “Yeah, let’s not talk about the fact the original Will Colfax novel got churned out during one of the most difficult years of my life.”)
So maybe all the advice people give about “clearing your head” before sitting down to write has some merit?  Or perhaps that’s why some people write better inebriated, as they’re too smashed to care about the emotional debris flying around in their head space?  Food for thought…