Because if they do, then my response is that we do not exist through reason, we cannot hope to be able to, and we should stuff that idea into the back closet and see what developments arise from freeing ourselves of it. Then. . . Well, if reason is not valid. . If it does not, then reason has something more to do with human beliefs, it is more arbitrary-like. But it is still the authority to which we refer when judging truth.
Reason shows it to be so.
So, onto your and Pascal's question. Well, I'll tell you, I don't think anyone can not guide their lives with reason. Many simple folks don't talk about or care about reason, but that just means that they don't use reason qua reason, they don't idolize, deify reason. But everyone uses reason. Reason, in essence, is careful decision making.