  A simple heuristic argument to understand the existence of branch points in
the unphysical sheet for pi-N scattering amplitude is presented. It is based on
a hypothesis that the singularity structure of the pi-N scattering amplitude is
a smooth varying function of the pion mass. We find that, in general, multiple
poles structure of a resonance is a direct mathematical consequence when
additional Riemann surface is included in the study and the two-pole structure
found to correspond to the Roper resonance is a good example.
