Some ethicists argue that we have obligations in virtue of our nature.
“You are a rational being. Rational beings are consistent. Therefore, you ought to be consistent.”
I suspect that they think they are modelling their argument on the following kind of argument.
“You are a trustee. Trustees act in the best interests of the beneficiaries. Therefore, you ought to act in the best interests of your beneficiaries.”
But I think their argument actually resembles the following kind of argument.
“You are Japanese. Japanese exhibit gaman (我慢). Therefore, you ought to exhibit gaman (我慢).”
The second argument is plausible because the role of a trustee is a creation of the law and that is in the background. The third argument is implausible because we do not have the same kind of normative background.
Some ethicists are no more rational than Japanese nationalists.