"On the one hand, a person's values are at least in part up to her, and are in this sense subjective: she can have a say in creating or inventing the kind of person it is worth her being. To be able to invent ourselves in this way is to have a kind of freedom that is distinctly human: a freedom not merely to control our actions but more fundamentally to govern ourselves; call this freedom "autonomy". Thus it is inconsistent with our autonomy that the source of the norms at issue in the kind of person it is worth our being be wholly external to us; rather, to be autonomous is for the source of those norms to be at least partially within one's understanding of who one is to be. In being autonomous, therefore, we can choose certain values, and by making these choices we determine our reasons.
On the other hand, there seems also to be an element of objectivity in what values a person holds in that she can deliberate about them correctly or incorrectly. Deliberation is a matter of choosing for reasons, thereby making possible the articulation of why one course of life is better than another, so that it is not intellectually arbitrary which values we choose. Hence through deliberation we can discover the values things really have and so the kind of person it is worth our being, potentially overcoming delusions or misunderstandings about ourselves. The possibility of such discovery means that there are rational constraints on which values we can autonomously choose.
... The problem is that such talk of rational discovery seems to leave no room for autonomous invention, and vice versa. How can we make sense of the possibility of getting our values (objectively) right or wrong when we are the ones (subjectively) determining the standards of correctness? This difficulty, which I shall call the apparent paradox of simultaneous autonomous invention and rational discovery, seems to undermine our best attempts at getting clearer on the kind of deliberation at issue here."
HELM, B. W. (2001). Emotional reason: deliberation, motivation, and the nature of value. Cambridge, UK, Cambridge University Press. pp.13-14.