  Heavy hadron spectroscopy was well understood within the naive quark model
until the end of the past century. However, in 2003, the $X(3872)$ was
discovered, with puzzling properties difficult to understand in the simple
naive quark model picture. This state made clear that excited states of heavy
mesons should be coupled to two-meson states in order to understand not only
the masses but, in some cases, unexpected decay properties. In this work we
will review how the naive quark model can be complemented with the coupling to
two hadron thresholds. This program has been already applied to the heavy meson
spectrum with the chiral quark model and we show some examples where thresholds
are of special relevance.
