plain the reason tortured Tantalus

Is baited by the fickle fruit, [and] declare

If merely brute caprice dooms Sisyphus

To struggle up a never-ending stair.   (5-8)

Tantalus, in Greek myth, is tortured in the underworld by being denied the opportunity either to eat or drink, even though both water and fruit seem clearly within his reach. Yet he can in fact reach neither: his situation, then, is “tantalizing” in the sense that the objects of his desire are visible but he is constantly denied them.

Sisyphus, in Greek mythology, is punished in the underworld by being forced to roll a huge boulder up a hill. When the boulder had been rolled to the very top, it inevitably rolls over and down the other side of the hill, thus forcing Sisyphus to repeat the process endlessly.  The speaker in Cullen’s poem compares himself to both Tantalus and Sisyphys.

These two classical allusions contribute effectively to Cullen’s poem in a number of ways, including the following:

• The speaker compares himself, as a black poet, to Tantalus because the speaker, even more than most poets, continually runs the risk of denial and disappointment.
• The speaker compares himself, as a black poet, to Sisyphus because the speaker, even more than most poets, continually runs the risk of frustration, of doing endless work without achieving any satisfying or enduring results.
• Ironically, Tantalus and Sisyphus were both being punished for actual infractions they had committed. Yet the speaker of Cullen’s poem has committed no wrong; he has merely been born black. Tantalus and Sisyphus arguably deserve to be punished; the speaker of Cullen’s poem does not.
• Ironically, Tantalus and Sisyphus were both punished by “gods” whom Cullen and most of his contemporaries would have regarded as mere figments of the human imagination. In other words, their stories are mere myths. The speaker in Cullen’s poem, however, sees himself as having been victimized, in a way, by the Christian God himself. The Christian God is typically associated with both mercy and justice, but the speaker of Cullen’s poem seems to think that he has been treated neither mercifully nor justly. His story, he suggests, is not a simple myth but a very painful reality.
• Tantalus and Sisyphus suffer only after they die, whereas the speaker of Cullen’s poem implies that he is suffering, as a black poet, even while he lives.

Countee Cullen's short poem "Yes Do I Marvel" contains two classical allusions, both to notorious criminals in the mythical world.

The first, Tantalus, was doomed to always be "tantalized" (the word comes from his name) by food and water which he could never reach. This punishment was a result of Tantalus trying to serve the flesh of his own son to the gods, who were understandably enraged by this.

The second, Sisyphus, tried to sexually assault the goddess Hera. As his punishment, Sisyphus has to push a boulder up a hill in the underworld. He never makes it to the top before the boulder rolls back down the hill again.

Although ancient sources explain why Tantalus and Sisyphus were punished, Cullen seems to view these odd punishments as evidence of the incomprehensible reasoning of God.

Cullen lived in America at a time when prejudice against African Americans was far more overt than it is now. Thus, Cullen ends his list of questions for God by wondering how God could "make a poet black, and bid him sing."