Mill’s “one very simple principle” is, at the point of statement, very simple indeed; the only circumstances in which mankind may interfere in the liberty of another is in the interest of protecting harm to others. No action may be taken solely due to the apparent interests of the person whose liberty would be interfered with. This ban on paternalism assumes a high degree of freedom and responsibility, and more than that, in order to be applied simply it seems to assume a very high degree of knowledge, and to discount the possibility of mental illness – at least that which cannot easily be tested. Feinberg attempts to account for this with his assertion that actions may be interfered with when a person is not acting voluntarily, or when it is not clear that they are acting voluntarily, and this is an appealing idea; when the hypothetical person is heading for the equally hypothetical damaged bridge, failure to ascertain whether or not they know that stepping on it will lead to death cannot be rectified after the fact. Interfering in their liberty whilst those checks are made may be odious, but it is merely temporary, and need not be seen as an infringement of Mill’s principle. Overall, the principle itself is indeed very simple; it is merely application in certain fringe circumstances which has any need to become anything to the contrary.