Why Adam?

Just an interesting thought, for those of you who care (Which is like three people). Why do pepole use the phrase "I don't know {Him/Her/It} from Adam."?
Of course you do. You know {Him/Her/It} from Seth, and Enos, Cainan, and Mahalaleel, Jared, and Enoch, Methuselah, and Lamech, and Noah. Who knows you may even know {Him/Her/It} from Ham, Shem, or Japheth.

Just a thought.