Enthusiasm is the cluster of emotions that motivate, that cause us to
act.
But, "discretion is the better part of valor".  Valor is both bravery
(the
inclination to act ... enthusiasm) and wisdom (the influence of all of
our
knowledge, experience and feelings ... judgement).

What's wrong with enthusiasm?  Most enthusiasm is not accompanied by
sufficient discretion.  Either knowledge, experience or feelings are
lacking, in most instances.