Sinister is just the Latin for left, and for a while the left was the good side. Roman augurs reading the birds are usually said to have faced south, which put the east and the sunrise on their left hand, so a sign on that side was a good one. Greek diviners are said to have faced north, which put the sunrise on the right and the dark on the left. Latin ended up carrying both verdicts, and English kept only the bad one. Nearly three thousand years of suspicion about the left hand may come down to which way a man was standing when he looked up.