A key dynamic in the crisis stressed by Mishkin(1997) is information asymmetry, manifest in the spread between risky and safe securities, the consequences of which(adverse selection and moral hazard) are ignored in the boom and come into play with a vengeance in the bust.
I would add one thing. Personally, I don’t just think it is “irrational exuberance” that leads to asymmetric information losing weight during a boom. I think that institutions form (reputations, organisations and the such) which appear to take care of the asymmetric information problem. However, when the downturn comes, and we discover that some of these institutions no longer exist/function we end up with a collapse.