How could human decisions actually be rational?

How can human decisions actually be rational?

Of course, people are influenced by their senses! I eat because I am hungry. So let's not put aside voluntary actions. I think what you are trying to say is that we don't seem motivated to act out of reason. Often we are motivated to act by factors such as passions (desires, emotions). The question then is what is the motivation for us to act: is it reason or is it passion? Philosophers of moral psychology have tried to answer this question. At present the question has divided them into humeans and non-humeans. As you can see by the name, David Hume's idea created a new field in ethics.

What's Hume's Idea? Hume argued that reason alone can never be a motive for voluntary action, that reason can never counter passions, and that reason is in fact the slave of passions. Hume's idea might sound like "Duh" to non-philosophers. But Hume's idea was revolutionary among philosophers. The reason was that philosophers up to Hume had been indoctrinated by the Socratic teaching that all we need to act is reason.

Under Socratic doctrine, we discover moral knowledge through reason, and once we have the knowledge it is impossible for us to act otherwise than what the knowledge tells us to do. Moral knowledge has the power to move us. For this reason, under doctrine, in the struggle between passion and reason, reason must have dominion over passions. In contrast, Hume argued that reason cannot move us. The reason is to discover knowledge. Scientific or moral, knowledge cannot motivate us to act. If so, the Humeans reply, why do people with the same (moral) knowledge behave differently?

The debate about who is the master and who is the slave continues.

See "Hume's Moral Philosophy" in SEP and "Moral Motivation" in SEP