The quality of your work should be excellent, of course, but your progress only has to be mediocre. You only have to meet extremely modest goals every week to reach success on your long-term goals.
Remember that mediocre is not a synonym of bad. Mediocre means middling, so-so, average. The ancient ideal of aurea mediocritas means a kind of golden moderation, avoiding either extreme.
(Remember too that many writers have extremely bad habits of procrastination, avoidance, irregularity of schedule. So mediocrity [having really good habits in terms of regularity, but not writing huge amounts all the time] is really way above average.)