In Carl Sandburg's poem, "They Will Say," the poet compares the "voice of the last cricket" to "one-kind of good-by." The comparison is likely chosen because both the cricket's voice and the act of saying goodbye are fleeting and bittersweet. The cricket's song is a signal that summer is coming to an end and winter is approaching, while saying goodbye often signals the end of something enjoyable and the beginning of something uncertain.
The setting for the "good-by" Sandburg is describing in his poem is not explicitly stated, but it is likely a rural or natural setting given the reference to the cricket. The setting may also be a place that is significant to the speaker, as saying goodbye is often associated with leaving a place or a person that holds special meaning.
Overall, the comparison between the cricket's song and saying goodbye highlights the transience of life and the inevitability of change. The poem suggests that even though goodbyes can be difficult, they are an important part of life and can be a source of growth and new beginnings.