Originally posted on 12/15/2012:

because the odds of each leg hitting is not equal to the odds you pay for the teaser

eg say a 2 team 6 points teaser is -120 (54.55% implied prob)

Lets say I tease Tampa +3.5 -110 With Indy +10 -115

Tampa +9.5 should be around -233.6 70.02% implied prob
Indy +16 should be around -224.8 69.21 implied prob

.7002 * .6921 = .4846 (48.6%)

so you are paying for something that hits 54.55% of the time when your two bets will hit 48.6 % of the time

of course there are some teasers that hit > what you pay