I was unable to finish the game on my first playthrough, thanks to being stymied by various bosses. The days ran out and the world ended--I'm an awful Savior. Square seems to have accounted for this eventuality by providing a New Game Plus option, which can be used even after abject failure. That let me retain my existing stat upgrades for a second run, which proved much easier with the leg up.
It's a smart workaround, but it also means Square must have known that finishing on the first try is difficult. I'm sure it's possible, but would probably require some level of foreknowledge about what to do and when. That means players might, like myself, find themselves failing the first playthrough to bring their stats into a second, and repeating some of the quests as a result. I found myself annoyed at that particular design decision, even if the feeling quickly faded as I sped through the missions I had already completed and felt much more empowered for the ones that had tripped me up.