What a fair price is, and why nobody knows one

The price at which a bet has zero expected value given the true probability. A genuine 50 per cent chance is fairly priced at +100; anything shorter is a loss and anything longer is an edge.

It is the reference point every other calculation depends on, and it requires a number nobody has. The true probability of a football game is not observable, before or after it is played.

This is why 'beating the market' is the only workable definition of an edge. Not because the market is right, but because it is the only benchmark that exists and the only one that can be checked afterwards.

The problem arrives next. A model that produces confident fair prices from historical data is producing an opinion, not a fact, and the confidence usually comes from the model rather than from the evidence.

What to do with it. Treat the de-vigged market price as the reference, and treat any disagreement with it as a claim you need a specific reason for.