You are speaking about some idealized philosopher's "rational," not the basic sense of "understands what they are doing," or as dismal put it: to fully understood the nature and implications of their actions. It's the opposite of delusional or psychotic i.e. "nuts."
I have high expectations of people who would call themselves rational. A lower bar, 'reasonable', might apply to them, but rational means putting forward an honest attempt to continually remove contradictions in someone's life. Someone can be reasonable without being rational. understanding the nature of a person's actions assumes an understanding of the nature of beliefs which those are founded on, including the fact that they are only beliefs, founded on nothing but their apparent necessity. The ability to recognize that a simpler set of beliefs is sufficient is part of understanding nature, including the nature of a person's own actions