You've set up a needlessly strong case to raise your supposed paradox.A question that raises for me is that supposing a player has an aim of exploring/expressing personal authenticity, and writes a belief that they do not have "I will always choose the right-hand path!" How can they pursue a belief that they do not have authentically? It requires them to choose actions (for their character) that they would personally not choose. It seems to require inauthenticity.
Go back to the GM's narration of the PC coming to a T-intersection. The player knows that there is no T-intersection - it's just imaginary! So how can they authentically reason about it? Hence authentic RPGing is per se impossible!
The dissolution of the paradox in my case also dissolves it in your case: the player is creating, and imagining. And in doing so is able to (or, at least, may aspire to) express themself authentically.