Why, exactly, are we supposed to get up, dust ourselves off, and try again? Of course, if you truly want something you shouldn't let failure get in the way. Sometimes, though, we wind up in darkness. The inky black where you can't see or remember wanting anything.
Sometimes, "meh" just covers over everything. There comes a time when you've been down in the pit so long you can't remember why you started climbing anymore. You try to call the memory to mind or imagine a reason to keep on climbing, but everything that shows up is covered in "meh." None of it seems worth the effort because the desire for it is too weak.