How does Vegas do it!?

How do they do it? But for the foregoing of an extra point in lieu of a two-point conversion to get within 8, the margin of difference in the Eagles-Bears game would have been 9 (19-10), the exact line posted by Vegas oddsmakers! How do they do it? How could they have foreseen the Eagles' difficulties in the red zone resulting in 4 Akers' FGs - and 2 misses! that would have well exceeded the line. Amazing! Now, I know it is the sports books that originally set the line but then it is adjusted accordingly based on the amount of "action" being wagered on either team in any given contest, so much of the credit goes to the collective wisdom of the sports betting public - half of whom thought the Eagles would win by more than 9 and half of whom thought the Bears would lose by less than 9. Collectively, then - we're all geniuses. Individually, however, is a totally different story. And I mean that in a totally why does it always seem like i'm losing way. At least this time I was on the winning side (as I noted in an earlier post when claiming the Eagles would cover the 9.) One incomplete two-point conversion is the difference between winning and losing. Amazing.