Georgia understimated Russia. Russia "over-retaliated"

Gary Brecher at Exiled Online sums it up well:
The fretting and fussing and sky-is-falling crap about this war is going to die down fast, and the bottom line will be simple: the Georgians overplayed their hand and got slapped, and we caught a little of the follow-through, which is what happens when you waste your best troops—and Georgia’s, for that matter—on a dumb war in the wrong place. We detatched Kosovo from a Russian ally; they detached South Ossetia from an American ally. It’s a pawn exchange, if that. If it signals anything bigger, it’s the fact that the US is weaker than it was ten years ago and Russia is much, much stronger than it was in Yeltsin’s time. But anybody with sense knew all that already.

But, before concluding thus, Brecher writes:
Most likely the Georgians just thought the Russians wouldn’t react. They were doing something they learned from Bush and Cheney: sticking to best-case scenarios, positive thinking. The Georgian plan was classic shock’n’awe with no hard, grown-up thinking about the long term. Their shiny new army would go in, zap the South Ossetians while they were on a peace hangover (the worst kind), and then…uh, they’d be welcomed as liberators? Sure, just like we were in Iraq. Man, you pay a price for believing in Bush. The Georgians did.