>>16691829 (OP)the dopamine neurons you have, are not all the same type
There are some dopamine neurons that ramp up slowly over time, and are good at maintaining motivation for long-term rewards. There are others that fire in a burst at any short-term reward. You need a mix of different ones to have a robust, healthy reward system.
You can read about this here:
https://neurosciencenews.com/dopamine-future-reward-29218/
What this means is that your brain probably trains and enhances the dopamine neuron subtype that matches the rewards that you are constantly encountering. If you want to get better at delayed gratification, you have to force yourself to ignore those tempting, immediate rewards. AND you can't just restrict yourself like a monk, you need to introduce real long-term rewards to your life and make sure you actually get them a few times and savor the moment, think about what it will be worth later if you are struggling, etc