What made Kisa Gotami understand the second time that she could not understand the first time?

When Kisa Gotami’s son died, she was so traumatized that she carried her son’s dead body from house to house asking people to heal him. One day, she went to Buddha who agreed to bring back the child if she brought a handful of mustard seeds from a house that had lost no loved one. She enquired far and wide fruitlessly. When she got tired she saw the flickering lights and realized how death was unavoidable. She had become selfish in her pain but understood that all selfishness must be given up.