  We address the question of minimal requirements for the existence of quantum
  bound states. In particular, we demonstrate that a few-body system with
zero-range momentum-independent two-body interactions is unstable against decay
into clusters, if mixed-symmetry of its wave function is enforced. We claim
that any theory in which the two-body scattering length is much larger than any
other scale involved exhibits such instability. We exemplify this with the
inability of the leading-order pionless effective field theory to describe
stable states of $A>4$ nuclei. A finite interaction range is identified as a
sufficient condition for a bound mixed-symmetry system. The minimal value of
this range depends on the proximity of a system to unitarity, on the number of
constituents, and on the particular realization of discrete scale invariance of
the three-body spectrum.
