I didn't mean it literally. I meant, everything on which we base our long-term plans.
For example:
You go to school, save up money, try to get a good job, try to advance in your career... on the belief that you will find the results rewarding. However, this is pretty easily dismantled if you're not a life-extensionist and/or cryonicist (and don't believe in an afterlife). All it takes is for you to have the realization that
1) If your memory of an experience is erased thoroughly enough (and you don't have access to anything external that will have been altered by the experience) then the experience might as well have not happened. Or insofar that it altered you through some other way than your memories, is interchangeable with any other experience that would have altered you in the same way.
2) In the absence of an afterlife, if you die all your memories get permanently deleted shortly after, and you have no further access to anything influenced by your past experiences including yourself. Therefore, death robs you of your past, present, and future making it as if you had never lived. Obviously other people will remember you for a while, but you will have no awareness of that because you will simply not exist.
Therefore, no matter what you do, it will get cancelled out completely. The way around it is to make a superhuman effort at doing the not-literally-prohibited-by-physics-as-far-as-we-know kind of impossible by working to make cryonics, anti-aging, uploading, or AI (which presumably will then do one of the preceding three for you) possible. But perhaps at an even deeper level our idea of what it is these courses of action are attempting to preserve is itself self-contradictory.
Does that necessarily discredit these courses of action?
First of all, I'm really glad we're having this conversation.
This question is the one philosophical issue that has been bugging me for several years. I read through your post and your comments and felt like someone was finally asking this question in a way that has a chance of being understood well enough to be resolved!
... then I began reading the replies, and it's a strange thing, the inferential distance is so great in some places that I also begin to lose the meaning of your original question, even though I have the very same question.
Taking a step bac...
Let's say Bob's terminal value is to travel back in time and ride a dinosaur.
It is instrumentally rational for Bob to study physics so he can learn how to build a time machine. As he learns more physics, Bob realizes that his terminal value is not only utterly impossible but meaningless. By definition, someone in Bob's past riding a dinosaur is not a future evolution of the present Bob.
There are a number of ways to create the subjective experience of having gone into the past and ridden a dinosaur. But to Bob, it's not the same because he wanted both the subjective experience and the knowledge that it corresponded to objective fact. Without the latter, he might as well have just watched a movie or played a video game.
So if we took the original, innocent-of-physics Bob and somehow calculated his coherent extrapolated volition, we would end up with a Bob who has given up on time travel. The original Bob would not want to be this Bob.
But, how do we know that _anything_ we value won't similarly dissolve under sufficiently thorough deconstruction? Let's suppose for a minute that all "human values" are dangling units; that everything we want is as possible and makes as much sense as wanting to hear the sound of blue or taste the flavor of a prime number. What is the rational course of action in such a situation?
PS: If your response resembles "keep attempting to XXX anyway", please explain what privileges XXX over any number of other alternatives other than your current preference. Are you using some kind of pre-commitment strategy to a subset of your current goals? Do you now wish you had used the same strategy to precommit to goals you had when you were a toddler?