I think we are talking past each other. I agree that life is volatile. And it is very lucky to be able to even plan a few years into the future.

But I do not think Graeber's quote is applicable here. The exercise of planning future cash flow can help you increase the quality of the bets you place (and/or adjust your expectations). Singular choices have no guaranteed results, but the sum total of choices can be influenced by gathering information about the world and keeping your models updated, allowing you to make choices where the odds are more favorable to you.