Irrelevant and invalid. In essence thesis is that individuals can't properly assess their ability to carry, much less the amount, of a proposed mortgage (or loan).

While this is a way to "look at" the Sub-Prime Mortgage Crisis, it makes no attempt, nor does it suggest a way to avoid the current or future similar crises. In essence the statement of the "expert" is no more than a recognition of the existence of a problem, the existence of which is not in dispute or questioned.