  We identify a simple physical mechanism which is at the heart of Asymptotic
Safety in Quantum Einstein Gravity (QEG) according to all available effective
average action-based investigations. Upon linearization the gravitational field
equations give rise to an inverse propagator for metric fluctuations comprising
two pieces: a covariant Laplacian and a curvature dependent potential term. By
analogy with elementary magnetic systems they lead to, respectively, dia- and
paramagnetic-type interactions of the metric fluctuations with the background
gravitational field. We show that above 3 spacetime dimensions the
gravitational antiscreening occurring in QEG is entirely due to a strong
dominance of the ultralocal paramagnetic interactions over the diamagnetic ones
that favor screening. (Below 3 dimensions both the dia- and paramagnetic
effects support antiscreening.) The spacetimes of QEG are interpreted as a
polarizable medium with a "paramagnetic" response to external perturbations,
and similarities with the vacuum state of Yang-Mills theory are pointed out. As
a by-product, we resolve a longstanding puzzle concerning the beta function of
Newton's constant in 2+{\epsilon} dimensional gravity.
