Full Idea
Even if we assume that reason prefers harmony between first- and second-order desires, there is no reason to assume that reason is on the side of achieving that harmony by changing first-order desires to suit second-order, rather than vice versa.
Gist of Idea
If first- and second-order desires conflict, harmony does not require the second-order to win
Source
Michael Smith (The Moral Problem [1994], 5.7)
Book Reference
Smith,Michael: 'The Moral Problem' [Blackwell 1994], p.145
A Reaction
[Smith is discussing David Lewis 1989 on second-order desires] Smith says that on the Humean view the rational winner should simply be the stronger of the two. Since this sounds like an endorsement for weakness of will, Smith relies on beliefs.