2008 was due to overconfidence.In reality I bet it was due to the actions of a small number of individuals, who gambled and lobbied to allow their gambling.
Overconfidence on the part of the borrowers that thought they would make enough money in raises to pay their inflated mortgage payments when the rates changed, and that, "surely a bank wouldn't approve me for more than I can afford! They're looking out for my best interest, not selling a product." Overconfidence on the part of lenders that thought they could keep bundling and selling marginal loans on the secondary market, and that their underwriting teams were doing their due diligence. Overconfidence that the market would keep rising at the rate it had been.
Everyone trusted someone else to be the gate keeper. And when the secondary market realized they were being sold garbage assets and stopped buying, and banks realized they were over exposed to marginal borrowers, it crumbled rapidly.
That's why I don't think a real crash is coming. In my very humble opinion, I'd guess the average buyer/borrower is much more qualified now than in 2008. Sufficient underwriting/due diligence, and not simply trusting everyone else to be honest, stabilizes the whole system.