CERTAINTY is a marvelous thing. It not only provides a useful carapace against the onslaughts of doubt; it also does wonders for one’s self-confidence. It is perhaps the one mental commodity that everyone, admirers and critics alike, will agree that the novelist-philosopher Ayn Rand (1905-1982) possessed in abundance. The attitude must be catching, for her disciples tend to be well endowed with certainty as well.