This might be all be easier to understand if you think about the power of “rewards” or “reinforcements”. For a behavior to continue or a new behavior to “take root” there must be rewards that “make us want to do it again”. Small pleasurable rewards are just as effective as more substantial ones if it matches the moment. We eat bad food if it contains the right amount of sugar or fat, which is the reward for the body (ah...short term). We are more likely to do a task if there is adequate “good feeling” upon completion. We are also more likely to pursue, or plan ahead, when we “anticipate” the reward to come and are more likely to persevere through adversity.
You can consciously build in adequate rewards, to give you the motivation you need, or increase your awareness of the rewards already there. Delayed gratification means forgoing the immediate “hit” for a more meaningful outcome further down the road (ie quit smoking, a pleasurable activity, for longer term health). Remember, we need short term and longer term reward systems to really improve our function and control.
At all times we are more controlled, in positive and negative ways, by the pre-existing systems of reward that are part of every thing we do, however minor the activity or behavior.