I reckon he just lost his initial enthusiasm for it when the scale of the task became clear. Better now than later. He had a very long honeymoon period here, but for many of us the gloss had rubbed off. I think that was mirrored in his own opinion of the job.
I don't find it surreal he left, I still find it surreal he was here at all. It's a bit like waking from a dream, not a good one or a bad one, but a strange one nonetheless.
I'm not angry or upset in any way. There were legitimate questions that he didn't have the required skill set. Clearly he didn't have the patience. He may not have realised that about himself when he took the job.
It might be a motivation for the new man to succeed where he didn't, or at least didn't see it out.
Now jog on Ancelotti. We'll manage.