I've often wondered why the words conscious and aware are synonyms, yet self-conscious and self-aware have such different meanings. Is there any reasoning behind this stark contrast in meaning between two compound words with such similar roots? Were their meanings always so different, or did usage cause their connotations to diverge over time?
Their roots weren't that similar:
Conscious was derived later, and came from Latin. Aware was derived earlier, and was derived from Old High German.
That's the reason for their difference in meaning.