  It is shown that field-theory based single boson exchange potentials cannot
be identified to those of the Yukawa or Coulomb type that are currently
inserted in the Schr\"odinger equation. The potential which is obtained rather
corresponds to this current single boson exchange potential corrected for the
probability that the system under consideration is in a two-body component,
therefore missing contributions due to the interaction of these two bodies
while bosons are exchanged. The role of these contributions, which involve at
least two boson exchanges, is examined. The conditions that allow one to
recover the usual single boson exchange potential are given. It is shown that
the present results have some relation: i) to the failure of the Bethe-Salpeter
equation in reproducing the Dirac or Klein-Gordon equations in the limit where
one of the constituent has a large mass, ii) to the absence of corrections of
relative order alpha log(1/alpha) to a full calculation of the binding energy
in the case of neutral massless bosons or iii) to large corrections of
wave-functions calculated perturbatively in some light-front approaches.
