You have to use something more like updateless decision theory rather than EDT or CDT: consider the similarity of your thought processes and decisionmaking to all the other people in a similar situation and act so as to further your goals given that a substantial fraction of similar people will ultimately make the same decision as you.

If I ever decide that it is no longer worth voting then I will probably leave the country under the expectation that other people like me giving up on voting are doing it for roughly the same reasons.