The other, the "speculative element, " is driven by sentiment and emotion: hope and greed and thrill-seeking in bull markets, fear and regret and revulsion in bear markets.
The narrative he builds is one that compels us to become more comfortable with math and statistics, one that suggests we should take advantage of machines where possible, and one in which we cannot lose the human element guiding the analysis if we want to avoid catastrophic chaos-theory driven failures to which machines are susceptible.