Odds x chance = 100%
If a team has 2.50 odds to win, the bookie is implying that, according to his calculations, that team has 40% chance of winning. There's often some discrepancy in the math and all the odds for an outcome, such as 1-X-2, don't add up to 100%; bookie shaves off a few percent as a margin depending on his greediness and often lowers the odds dynamically as whales start dumping tons of cash into an outcome. No matter what odds players bet on, the bookie is guaranteed at least some winning to keep the show running because the human brain sucks at predicting probability.
There's a lot of complex math that goes into setting any given odd but the key takeaway is that the bookie is always estimating. If you bet for a longer period of time, you'll notice that bookies (at least those that stay in business) are actually pretty good at estimating chances. You can estimate too, and if you can estimate better than the bookie, you'll be having a consistent way to win.
Your goal is to find such odds on such events where your information beats bookie's. The trick is to understand bookies are human too and they have to process thousands of odds on a typical day, with a small percentage of them being botched for any number of reasons. Bookies know they make mistakes but are counting on the average bettor making more mistakes due to what I call "emotional betting" i.e. fixation on a preconceived notion of what he wants to happen rather than the facts at hand. Grooming a set of skills that will help you curb emotions, get rid of wishful thinking and find reliable sources of information then becomes crucial in discovering which odds are valuable.
At one point, one of my distant cousins was playing for an Italian basketball team. He told me that his team would intentionally turn off the heating when playing at home, making the away team sluggish in the 1st quarter until they warmed up through playing. This gave home team enough time to make a comfortable lead, though their gameplan would tend to fall apart later in the match, meaning the home team would start leading against stronger teams but then lose. This is the kind of information you can learn and account for that the bookie has no idea exists. Being a small bettor, you can outmaneuver the bookie and make just enough leverage to consistently win at betting as long as you use your brain.
The implication here is that there are plenty of obscure but valid information sources that you can compile into a big(ger) picture to get a 3D picture of the event rather than a 1D or 2D one as presented by a monolithic official source. When everyone goes with the same information source is when you get catastrophes as people en masse extrapolate 1D (vectors) into 3D (objects) to lose their savings and their minds. To me, this isn't just an abstract philosophical lesson but an actual, mathematical rule that's easily testable in practice: a variety of information sources creates a much stronger conclusion that's based in reality, not wishful thinking. The trouble is, that conclusion can sound completely deranged but still be valid.
The goal of any bettor is to find such bets where he's almost guaranteed to win, regardless of the odd. For example, consider the following three investment opportunities aka bets:
As a bettor, which one should you choose? If you said the 1% one, you are wrong; if you said the 50% one, you are again wrong; you should always go for the investment that's most likely to land, not the one that's most likely to make you rich. They all average out at breaking even, but only the 90% one can make you any money because your budget can't match the bookie's. If you play risky bets you're guaranteed to go bankrupt long before the bookie because the dice roll or the coin flip or whatever doesn't remember what happened earlier and a 1% chance of something happening will always remain a 1% chance. Go for the safe bet, dummy.
The worst part about the 1% bet is that it's going to land at some point through sheer luck, making you a load of money that will convince you that betting pattern is great, all it has to do is repeat again and again, which it won't. You will then bet again with the winnings, losing all you've got. This is how most "winners" on betting gamble away their fortunes, as they imagine all it takes is one more doubling of their investment and they're in the clear. It's not going to happen and statistically you should be on firm ground, choosing the safe bet.
Now here's a shocker: safe bets don't always have the worst odds. Just because a bet has 1.10 odds doesn't mean it's safe but also because it has 2.50 odds doesn't mean it's a 40% gamble. You should use your brain to determine which result is the safest bet and then bet a feasible amount that won't bankrupt you. Take care of dues and only gamble with what you can afford to lose.
I use betting as a cheap, affordable and legal method to test my information-gathering methods and just have some fun; if you can find an equivalent to this, definitely do it as the lessons learned will give you a massive advantage in palpable ways. The exact same idea of delaying your choice until you've gotten enough varied information that you can make a multidimensional choice can be applied to buying a house, investing into stock market, choosing a partner, taking out a loan or just choosing a college. It's a game and like all games it's used as a preparation for the real thing.