You probably know Cain as the bad guy who (for no good reason) killed his nice and kind brother Abel in Genesis, in the world's first murder. Some of the unexplained problems of this account (such as why God accepted Abel's sacrifice but not Cain's, which is what pissed Cain off in the first place) are answered in the apocryphal book of Enoch. Interestingly, the Book of Enoch also suggest another motive as well: Adam was planning ...