Two failures, and neither is the kind you find by being careful with arithmetic. The first is about dimension. A planar grasp analysis is cheap and everyone reaches for it, and the standard worry is that it will be optimistic: coplanar contacts obviously cannot resist a wrench out of their plane, so the spatial quality should collapse to zero. Measure it. The rank is six, not three, and the spatial wrench ball is positive. The reason is one line of algebra: at a contact whose normal lies in the plane, the tangent direction given by normal cross t-one points OUT of the plane, so the friction cone contains out-of-plane force. The grasp is not degenerate. So is the planar number optimistic or not? Neither, reliably. On this sphere it reads nine-tenths of the spatial value at three contacts and eleven-tenths at four. The direction depends on the arrangement, which makes it useless as a safety factor in either direction. What IS consistent is more interesting and more actionable: as you add coplanar contacts the spatial ball does not move by one part in a billion, while the planar number climbs by twenty per cent. A designer optimising the cheap metric adds fingers, watches the score improve, and has bought nothing. The second failure is about state. Coulomb friction has two states, stuck and sliding, and real elastic contact has a third that sits between them for most of the useful range. As tangential load rises, a slipping annulus eats inward from the rim of the contact patch and the stuck core shrinks. Its radius goes as the cube root of one minus the load ratio, so the AREA goes as that squared - and a cube root near one is brutally steep. At a tenth of the friction limit the stuck area is already down to ninety-three per cent. At half, sixty-three. A monitor watching for gross slip sees nothing until the ratio hits one, by which time the object is leaving. A monitor watching the stuck area warns at under half of capacity, from the same sensor.