I'm not into horses but the odds are based on opinions just like sports betting and they're not definite.
The outs in poker are definite. There are only so many cards in a deck and only so many cards that can help your opponent or help you improve your hand.
You have to know there are 52 cards in a deck. There are only 4 of kind cards and 4 suits and you have to be able to count how many are outs are available to help you.
If you want to really understand outs then play stud, stud8 or razz on
pokerstars with play chips. You start a hand and the cards you might need are literally staring at you on your opponents boards.
So if you have an ace in the hole(not showing) but your opponents are showing the remaining 3 aces on their boards then guess what? You're not to pair that ace!!! Its that simple.
Omaha and Holdem don't show opponent cards so you should assume they're still available but then you learn what
hands people usually play then use deductive reasoning to eliminate cards since your opponent probably are holding them but that takes skill.
You have to know basic outs and that's easy to figure out with basic math that you can do on your fingers and some practice then you have to weigh the odds.