Why the credit crunch has lasted so long?

The comment on this Economist's article
http://www.economist.com/finance/displayStory.cfm?story_id=12010659&mode=comment&intent=readBottom
from "The Big Picture" is worthing reprinting here in full:
"Suggesting that the duration of the credit crunch is due to two of its symptoms, misses the point. We are in a classic major financial unwinding. Which always follows massive asset inflation driven by massive credit inflation. Easy to see in history and easy to understand.One of these two symptoms of the real-estate implosion is but one of many asset classes where the valuation of the asset is falling through the debt level incurred to acquire it. The other, of inflating commodities is a symptom of the attempted fix, of throwing more credit to fix a problem of excessive credit. As the money is poured into the financial system, it certainly doesn't go to the loosing games, but rather to the few remaining hot stories. Primarily food and oil, which feed directly into consumer inflation. But this is only a transitional response, until the unwinding accelerates to the point of full deflation in all asset classes.It is classic, text book stuff. There have been five such event in the modern financial world over the past 300 years. This is the sixth.This credit crunch is just beginning."
Debt deflation is why the great depression of 30s happened, it is also why we are in a credit crunch.