From a purely psychological and physiological standpoint without considering what desires are chosen by a society's norms and the like:
Functional imaging of the brain has shown that self-control is correlated with an area in the dorsolateral prefrontal cortex (dlPFC), a part of the frontal lobe. This area is distinct from those involved in generating intentional actions, attention to intentions, or select between alternatives. This control occurs through the top-down inhibition of premotor cortex. There is some debate about the mechanism of self-control and how it emerges. Traditionally, researchers believed the bottom-up approach guided self-control behavior. The more time a person spends thinking about a rewarding stimulus, the more likely he or she will experience a desire for it. Information that is most important gains control of working memory, and can then be processed through a top-down mechanism. Increasing evidence suggests that top down processing plays a strong role in self-control. Specifically, top-down processing can actually regulate bottom-up attentional mechanisms. To demonstrate this, researchers studied working memory and distraction by presenting participants with neutral or negative pictures and then a math problem or no task. They found that participants reported less negative moods after solving the math problem compared to the no task group, which was due to an influence on working memory capacity.
But indeed you already knew that, so moving forward, temptation interferes with self control. Temptation is sometimes based on pleasure or power. Therefore the pleasure centers of the brain (such as the nucleus accumbens, ventral pallidum, orbitofrontal cortex and anterior cingulate cortex) may sometimes act in opposition to the frontal cortex.
But that's not all:
Self-regulatory failure is a core feature of many social and mental health problems. Self-regulation can be undermined by failures to transcend overwhelming temptations, negative moods and resource depletion, and when minor lapses in self-control snowball into self-regulatory collapse. Cognitive neuroscience research suggests that successful self-regulation is dependent on top-down control from the prefrontal cortex over
subcortical regions involved in reward and emotion. We highlight recent neuroimaging research on self-regulatory failure, the findings of which support a balance
model of self-regulation whereby self-regulatory failure occurs whenever the balance is tipped in favor of subcortical areas, either due to particularly strong impulses
or when prefrontal function itself is impaired. Such a model is consistent with recent findings in the cognitive neuroscience of addictive behavior, emotion regulation
-Cognitive neuroscience of self-regulation failure