Truth, or the better answer? The truth is, there are days where I feel like I can't write. On those days, you'll probably find me in my PJ's, binge watching shows like Outlander or Castle, and eating popcorn with M&M's poured in the bowl.
But the better answer is that you may be blocked for writing your current work in progress (WIP), but you should try writing something else just to keep you writing. I find that if I don't write at all in a day, it makes going back to writing the next day even harder. Because who wouldn't want to have two days of total show or movie bingeing? Or maybe 3? And before you know it, you haven't written anything over an entire week.
Think about it this way—writing 100 words is 100 words more than you had. Add up 100 words at a time again and again, and eventually you'll have a completed WIP!