“Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them.”
David Hume
A Treatise of Human Nature (1739).
ed: L.A. Selby-Bigge, M.A. (Oxford: Clarendon Press, 1896)
Book II, Part III, Section III

Long intellectual debates within
Decisions and beliefs at the end of lengthy reasoned chains
The very control of action
Intellect, reason; these claim control
But what wills the will.