  Contrarily to a common belief, any beam of light possesses to a some extent
the ability to "reconstruct itself" after hitting an obstacle. The celebrated
Arago spot phenomenon is nothing but a manifestation of this property. In this
work we analyze the self-healing mechanism from both a mathematical and a
physical point of view, eventually finding a new expression for the minimum
reconstruction distance, which is valid for \emph{any} kind of beam, including
Gaussian ones. Finally, a witness function that quantify the
self-reconstruction capability of a beam is proposed and tested. The results
presented here help clarifying the physics underlying self-healing mechanism in
optical beams.
