Edge case

An edge case is an unusual or extreme situation your product has to handle correctly even though it rarely happens, an empty list, a name with an apostrophe, a payment that fails halfway, a user who clicks twice. The happy path is what you imagine when you design a feature; edge cases are everything else reality throws at it. For a lean founder, edge cases are where quality is quietly won or lost. Software that only works when everything goes right feels flaky and erodes trust, because customers inevitably do the unexpected. The discipline is to map the full state matrix before building: for every action, ask what happens when the input is empty, invalid, duplicated, or interrupted, and design a sensible response for each. You will not catch every edge case, but deliberately handling the obvious ones, especially around money and data, is what separates a product that feels solid from one that feels fragile.