Exactly. And when you're 100% certain, so is Vegas, and there's really nothing to gain and everything to lose.
The one game I cam VERY close to betting last season was the New England @ Denver Broncos game. I think they only had NE favored by 6 or so. I knew that wasn't enough, and that even Vegas was all twisted in its obsession over Tebow. I spooked myself out of betting it that morning (and I was going to do something like $2,000-3,000). Sure enough they went in there and beat the absolute hell out of the Broncos.
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"I don't get sick. I don't observe major holidays. I'm a jackhammer." - Jim Harbaugh & Dwight Schrute