A melancholy thought about playing the races can be stated simply and succinctly. If your opinion is the same as the betting publics, you have no edge, and therefore no bet.
Remember this:
The best bet at the racetrack, every race, every day, is:
A horse having a strong chance to win at attractive odds.
A horse having a strong chance to win at fair to poor odds is less attractive.
A horse having a weak chance to win at attractive odds is least attractive.
Never bet the underlays. It's the first axiom of pari-mutuel wagering.
Two terms are basic:
Underlay An overbet horse
Overlay An underbet horse
As most people know, at the races the handicapper is playing against the crowd, which sets the odds with their wagers. The handicapper's task is to establish a personal betting line which can be compared to the crowd's.
Making a betting line is a skill that develops with experience. It is best done analytically or intuitively, using all the handicapping factors that apply to the race, not mechanically or mathematically, using a few handicapping factors of choice.
When the handicapper decides the crowd has made a mistake, that's an edge, and it's time to play.
If you believe a horse should be 5/2 and the odds are 7/4, that's an underlay, and no play. In the same race, if your 2nd choice is 3/1, and the odds are 5/1, that's an overlay, and an excellent play
The difference is the difference between losing and winning.