We investigate what are the key physical features that cause the development
of a naked singularity, rather than a black hole, as the end-state of spherical
gravitational collapse. We show that sufficiently strong shearing effects near
the singularity delay the formation of the apparent horizon. This exposes the
singularity to an external observer, in contrast to a black hole, which is
hidden behind an event horizon due to the early formation of an apparent
horizon.Comment: revised for clarity, new figure included; version accepted by Phys.
Rev. D (RC
