In the poem "Keeping Quiet," the poet Pablo Neruda refers to the sadness of never understanding oneself and nature. Human beings are so busy with their daily activities that they have no time for introspection, which can lead to death or destruction. This lack of understanding darkens their ways with distress and wretchedness. The poet also finds it sad that people fail to understand themselves in the monotonous everyday existence. In summary, the sadness that the poet refers to in the poem is the sadness of failing to understand oneself and nature due to the frenzied activities of daily life.