A repeatable reason your trades should have positive expectancy over many attempts; without one, trading is paying spread to gamble.
Expectancy: the average trade. Forty trades sorted by outcome: 24 small losses and 16 larger wins. Weighting each side by how often it happens gives the average result per trade, marked here by the dashed line at +$120.
An edge can come from information, speed, a structural inefficiency, superior risk-management, or patience that others lack. It must be small enough to be believable and large enough to survive slippage and costs.
Most retail edges are behavioral: being willing to sit out, take small losses, and hold winners while others do the opposite. An edge is proven by a trading-journal over a real sample-size, not by conviction.
Example: a setup that wins 45% with 2R average winners has an expectancy of +0.35R. After 0.1R in costs it is +0.25R. That is an edge. The same setup at 40% and 1.5R is +0.0R after costs, which is not.