  The full treatment, both nonperturbative - through O(1/m_c^3) - and
perturbative - through O(alpha_s) and BLM type O(alpha_s^2) - of the
semileptonic lifetime of the D meson is given. A dedicated discussion of the
numerics involved is made, with the result that the leading order prediction
plus corrections fail to match experiment. To explain the difference, a model
of duality is invoked, where it is shown that the asymptotic nature of the
nonperturbative expansion may be responsible for the theoretical experimental
discrepancy. A particularly interesting conclusion which follows from the model
is that any attempts to extract alpha_s from tau decays are doomed, since the
same duality violating mechanism is at work here.
