What does “punishment” mean at Gen 4:13 and why is it greater than Cain can bear?

The word translated here “punishment” is עָוֹן or avon, glossed as “iniquity” or “punishment for iniquity.” As the word his this double-meaning, Cain’s suggestive statement is not merely a lament for the woes to come; it means, essentially, that the severity of the sentence has revealed to Cain, only too late, just how enormous his crime was.