What is an edge?
An 'edge' sounds mysterious, but it's a simple idea: you have an edge when your opinion about a game is better than the book's price. You don't need to win most bets — you need to be right slightly more often than the odds expect.
Your guess vs the book's guess
Imagine your research says a team wins 55% of the time. The book's price (after removing their fee) implies only 50%. You disagree with the book by 5 points, in your favor. Every time you can bet at a price that's 'too cheap' compared to your own estimate, you're getting value.
Winning over time (expected value)
Let's do the math with easy numbers. If you're right 55% of the time and you bet 100 at even odds (+100): 55 times out of 100 you win 100, and 45 times you lose 100. Over 100 bets that's +5500 − 4500 = +1000, an average of +10 per bet. Some individual bets will lose, but the edge shows up over many bets — that's why patience matters.
Where the profit really comes from
Your profit doesn't come from predicting every game perfectly. It comes from consistently betting when the book's price is worse than your own honest estimate. It's like a store that sometimes sells $100 bills for $95 — you lose money on fakes occasionally, but if you only buy the real ones at a discount, you make money over time.