  Recent developments in hadron spectroscopy triggers the discussion on various
exotic configurations beyond the simple three-quark state for baryons and
quark-anti-quark pair for mesons. In particular, the states observed near a
two-hadron threshold are often regarded as candidates of hadronic molecules,
which are made of constituent hadrons and dynamically generated by the hadronic
interactions. However, identification of the hadronic molecules involves
several subtle difficulties which are often overlooked or underestimated. Here
we summarize these subtleties and present a promising approach to distinguish
the dynamically generated states from others using observable quantities.
