  We address the question of why larger, high symmetry crystals are mostly
weak, ductile and statistically sub-critical, while smaller crystals with the
same symmetry are strong, brittle and super-critical. We link it to another
question of why intermittent elasto-plastic deformation of sub-micron crystals
features highly unusual size sensitivity of scaling exponents. We use a minimal
integer-valued automaton model of crystal plasticity to show that with growing
variance of quenched disorder, which can serve in this case as a proxy for
increasing size, sub-micron crystals undergo a crossover from spin-glass
marginality to criticality characterizing the second order brittle-to-ductile
(BD) transition. We argue that this crossover is behind the non-universality of
scaling exponents observed in physical and numerical experiments. The
non-universality emerges only if the quenched disorder is elastically
incompatible and it disappears if the disorder is compatible.
