I think that there is a reason for everything. At least there is for the things that I do. I can explain with a simple example.
One time on Facebook. I made a status update containing one word. The word was “potato”. I bet that no one will ever guess exactly why I did that but I know the reason. A certain Hy-Vee employee also knows about an event concerning a potato. No one knows exactly what happened to that potato but I know that a customer bought it. They probably ate it too.
But does anyone really need to know the reason that I write about that potato? No, it is irrelevant to everything else I do. The point is that there is a reason.
Reason is not only used as a noun. It is also a verb. It means to think about the reasons that things happen or what might happen. Since thinking is relevant to me, it makes sense to say that to be able to reason about reasons is relevant.