Why mine warfare rewards one lucky weapon

Public memory overweights the mines that hit ships and rarely records the hundreds successfully swept or the passages completed safely. A field of roughly a thousand mines can be mostly cleared and still produce a strategically important loss if one remaining weapon finds a battleship. This asymmetry makes mining cheap and comparatively low-risk for the laying force, especially with submarine minelayers. In the Adriatic, both Austria-Hungary and Italy used mines, so claims of one navy's incompetence can miss how inherently unforgiving the weapon was.