Collision detection is deceptively difficult. It's also a problem in engineering simulations. For example, deep drawing where the material bends and slides over the surface of the tooling can go wrong at a sharp corner which might be missed by the contact detection. Even without those, it can get affected by artificial irregularities due to the discretization of the surface. There are workarounds like adding some elasticity to allow a bit of give or extending the detection region a little beyond the edge of the geometry to ensure corners are fully covered, but they're pretty ugly hacks that introduce their own errors. Analysists sometimes have to manually tweak the fudging parameters by trial and error. It's an awful situation.
