As nearly all professional bettor will tell you, backing heavy favourites is a sure fire way to the poorhouse. That’s common knowledge, right? Perhaps, but there’s one problem with that type of thinking: it’s dead wrong.

The received wisdom is the linesmakers skew their odds on heavy favourites since the public love betting on the best teams. The bookies no doubt see a flurry of parlays involving clubs like Chelsea, Barcelona and Juventus every weekend. Surely there’s value in taking the underdog in these situations, isn’t there?

Actually, numerous studies have shown that blindly backing long shots is a losing proposition in the long term. To find out why that is the case, we have to discover how a bookmaker operates. Since the bookies take most of their action on short-priced favourites, it’s often assumed they can be exposed to big liabilities if all the hot teams win. Even though this is sometimes the case, and many bookmakers suffer months of huge losses, you can find a number of ways a bookie can protect himself.

It is critical to do not forget that most heavy favourites are combined in parlays involving at least three teams. A bookmaker only needs one loser to take his customer’s money. As a result, there is little need to lower the odds on a “public” team. Many sportsbooks will even inflate the odds of a hot favourite to attract new customers, safe in the knowledge that parlay players will not hurt their bottom line.

If the favourite’s odds are an accurate reflection of it’s true probability of winning, the bookmaker must make adjustments elsewhere. That usually means offering worse odds on the underdog and also the draw. Understanding the concept of theoretical hold might make this clearer.

When designing lines, a sportsbook will offer odds on each team that offer it a slight edge, ensuring a profit no matter how the game turns out. This really is called the Theoretical Hold and is expressed as a percentage. It represents the combined amount of customers’ bets that the bookmaker expects to keep.

It’s called theoretical because in reality a bookmaker rarely has balanced action on all sides. If a bookie takes the bulk of his bets on a heavy favourite, he can offer it at a far more generous price and similar site accept a smaller profit margin. Short-priced favourites generally have small margins, but high volumes. Bigger odds mean bigger margins. There is little incentive for a bookie to offer competitive odds on a big underdog if he doesn’t expect much betting interest in that team.