Understanding Classical Rationality at a Basic Level
After all,suppose person A knows they will derive satisfaction from honoring sunk costs. Then doesn't honoring sunk costs make them better off (it fulfills their desire for happiness), and therefore becomes rational for person A?


Utility experienced from honouring sunk costs is treated separately from honouring sunk costs themselves. ( section 2 of http://www.princeton.edu/~tkelly/papers/Sunk%20Costs,%20Rationality,%20and%20Acting%20For%20the%20Sake%20of%20the%20Past.htm )

If I feel good for rescuing my phone from a toilet, or feel bad, that’s separate from the phone being in the toilet.