What does Genesis 4:11 mean?
When Adam sinned, God pronounced a curse on the land on which Adam would have to work (Genesis 3:17–19). Here, as well, God pronounces a curse on both Cain and on the ground in response to Cain's sin and rebellion.The beginning of this curse is that Cain, himself, would be "cursed from the ground." Cain had murdered his brother in the field. The ground had received Abel's blood. In a form of poetic justice, the ground would no longer give back to Cain any crops. Cain's days of working the ground to make a living for himself were over. This punishment fits the crime on several levels. It was Cain's offering—presumably inferior—of crops which displeased God in the first place (Genesis 4:3–5). Cain's choice not to obey, but to dig deeper into sin, resulted in him losing everything.
Losing his livelihood was a threat to Cain's continued existence, but it isn't the end of his curse.