A counterexample to the originarity of reasons in "What we Owe to Each Other"

In his book from 1998 - What we owe to Each Other - T.M. Scanlon argued that the concept of reason is a primitive one when it comes to explain every course of action that might be morally relevant. Relying on an intuitive pattern of explanation for what it is for something to be a reason Scanlon argues that any such consideration will always lead back to the same idea: a reason is a consideration that counts in favor of something. And it counts in favor of something by providing a reason for it. It seems as if we have reached the definitional bedrock of reasons. I believe Scanlon left out of consideration typical courses of human action, that not only would be wrongly described as "rational", but whose agent itself would systematically fail in providing reasons to explain both his behaviour and a resulting action or course of action. In this paper I will be focusing my attention on the case of weakness of will as a possible counterexample to Scanlon's proposal.