Final answer:
The line from Countee Cullen's poem that best reveals the universality of human suffering is 'the ever-threatened truth that each and every man, on the foundation of his own sufferings and joys, builds for all,' highlighting the shared nature of human experiences.
Step-by-step explanation:
The question asks for a line from Countee Cullen's poem "Any Human to Another" that captures the universality of human suffering. The provided excerpts from various sources speak to themes of empathy, compassion, and the shared experiences of suffering and joy. One line that stands out from Cullen's poem which encapsulates this universality is:
“the ever-threatened truth that each and every man, on the foundation of his own sufferings and joys, builds for all.”
This line suggests that our personal experiences of suffering and joy contribute to an overarching human experience, where empathy is born from recognition of our shared humanity. The sentiment reflects a common bond among people, regardless of differences, and recognizes that suffering is a universal aspect of the human condition.