I think that it is important in any analysis of Jackson's short story not to lose sight of the victim, Tessie Hutchinson. While there are many different approaches to take in analyzing the story, one should not forget the fact that she is the victim of the community. Little can take that away. With this in mind, I think one of the sad ironies of the story is her enthusiasm at the start of the narrative. Tessie enters late, with a combination of excitement and underlying remorse for "almost" missing the ceremony. She enters with her declaration to Mrs. Delacroix, her best friend, that she almost forgot what day it was. Tessie's excitement and zeal in attending and being part of the lottery, and the community, in general becomes ironic given how the plot turns in the middle and end.
To some extent, I think that this is deliberate on Jackson's part. The irony of Tessie's enthusiasm reflects how there is a joy in being part of the community, any community. Human beings like to be included, enjoy the connection to others and to one another. The fact that Tessie likes this is, in itself, not ironic. Yet, it becomes ironic when she recognizes that while there is joy in being part of the community, there exists a countervailing force of terror when one is being hunted down by it. Perhaps, this irony is Jackson's way of reminding us, the reader, the widen our scope of compassion for others and to not be so blindly driven by the seduction of inclusion at the cost of what happens to those who are excluded. Given how Jackson is painfully aware of the Holocaust and the spread of Communism, this irony is not lost on either her or the reader.