Walt Williams Neck wrote:
Big races at Prairie Meadows again....I need McCraken to win and pay $160 to make money on my ROI

Again, you scoff at something you don't understand.
The expected ROI compares the theoretical odds to the market or live odds. If that relationship is negative, the horse is a bad bet, because if you ran the race X number of times, you would lose money, even if you won the one time. If the relationship is positive, then the horse has value and represents a good bet, generally speaking. The good bets have to be considered within the context of the field and other variables. Maybe the horse has a positive expected ROI as a 5th or 6th choice. That doesn't make it necessarily a good bet, if the horse is going against tough competition. It's all relative.
If you are betting the live odds favorite all the time, then there's a good chance you are making bad bets, because these are the horses that typically are overbet. You don't often see the live odds favorite as overlays. Most of the time they are underlays. In some races, you may have only one or two horses that are true overlays. This is the dirty little secret about horse racing, in that the odds setups of horses are against the better and in favor of the house to win. That's why I say you need to wait for the right setups of odds. If the odds are not there, the race is a fold. All these things can be demonstrated mathematically.