But if, in practice, the only realistic way to make better-enough decisions to actually realize that 55% is to receive a letter from your future self telling you whether it was good or bad, then "wanting to make the 55%" is irrelevant.

It is frequently clear in hindsight which decisions were better, but the point of hindsight is that you have information you did not have when you made the decision—and, in most cases, could not possibly have without violating causality.