At the end of the chapter, what metaphor does Achebe use to illustrate Okonkwo's belief about his son

"He sighed heavily, and as if in sympathy the smouldering log also sighed. And immediately Okonkwo's eyes were opened and he saw the whole matter clearly. Living fire begets cold, impotent ash. He sighed again, deeply."

Here Okonkwo considers that a man with such intensity and fire as he, begets (has children) that are weak like the ash from the fire.