  Leibniz said "Naturam cognosci per analogiam": nature is understood by making
analogies. This statement describes a seminal epistemological principle. But
one has to be aware of its limitations: quantum mechanics for example at some
point had to push Bohr's model of the atom aside to make progress. This article
claims that the physics of granular packings has to move beyond the analogy of
frictionless spheres, towards local models of contact formation.
