Does it therefore mean that the outcome of an investment can be determined in advance when we delay enjoyment/gratification?
Delaying gratification is meant to save things, not to achieve any certainty in the future. We choose so because we believe that the present is worth sacrificing for the greater good in the future. It is a different causality between delaying gratification with a determined investment return. So, just because someone is working hard in the present doesn't mean any investment they make would be profitable yet ahead in the future.
Correct, and yet the ones that are working hard now, saving and investing for the future have way greater chances of achieving a favorable future for themselves and their families, and the most interesting thing about this is that this characteristic can be observed from a very early age, kids which show they can delay their gratification have been shown to do way better later in life even if their starting conditions were not optimal, so this should give hope to those which want to achieve financial success later in life.