Over going to Arkansas? Well, I think he had illusions of creating his own program with its own identity and stepping out from Alvarez's shadow. What he doesn't realize is that's a hell of a lot harder to do without the infrastructure in place that he had benefited from at Wisconsin. He really felt as though he never got enough credit for his "success" (if you want to call it that) and it would never be his program. To a certain extent that's understandable.
So, he viewed the Arkansas situation as a chance to show everyone he could do it on his own against the Alabamas and LSUs of the world. I'm sure he realized it would not be easy, but I also don't think he thought it would be such a rough first season. He was given some leeway this year because he's a first-year coach, but he won't get as much slack if they continue to struggle, especially with how much dough they're giving him.
On the surface, Wisconsin and Arkansas are
relatively comparable programs. Both are the only major programs in the state, both have had their ups and downs, etc., etc. But here's the thing: Arkansas fans are CRAZY. We're not talking your regular SEC-type nutjobs; these people are a special brand of loony. It's not hard to find
example after
example of this. Plus you've got Jerry Jones breathing down your neck. I'd be surprised if Bret lasted more than three seasons down there.
TL;DR He may not be an "imbecile" per se but he didn't exactly think through the move he made last winter.
P.S.
This thread does a pretty good job summarizing, in retrospect, how a lot of Wisconsin fans felt about the news. Some stuff is NSFW.