  The influential theorems of Hawking and Penrose demonstrate that spacetime
singularities are ubiquitous features of general relativity, Einstein's theory
of gravity. The utility of classical general relativity in describing
gravitational phenomena is maintained by the cosmic censorship principle. This
conjecture, whose validity is still one of the most important open questions in
general relativity, asserts that the undesirable spacetime singularities are
always hidden inside of black holes. In this Letter we reanalyze extreme
situations which have been considered as counterexamples to the cosmic
censorship hypothesis. In particular, we consider the absorption of fermion
particles by a spinning black hole. Ignoring quantum effects may lead one to
conclude that an incident fermion wave may over spin the black hole, thereby
exposing its inner singularity to distant observers. However, we show that when
quantum effects are properly taken into account, the integrity of the
black-hole event horizon is irrefutable. This observation suggests that the
cosmic censorship principle is intrinsically a quantum phenomena.
