The two minor challenges feed the Main Challenge, which is the absolute difference between them and is read as the deepest and most persistent obstacle of a life, present throughout rather than confined to a season. The Second Minor Challenge is thus both an influence in its own right and a component of the central one. Like the whole challenge scheme it is computed by subtraction, the deliberate inverse of the additive core numbers, and it belongs to the modern American system, resting on the conventions by which month, day and year are reduced to single digits.
Underwood Dudley's critical survey of the system, Numerology: Or What Pythagoras Wrought, treats the Main Challenge this figure feeds into as a good example of how the modern chart builds ever more derived numbers from a small set of birth-date and name totals; the scholarly verdict on the system's claimed Pythagorean descent, that it has been largely abandoned as a comparative category, applies to this derived layer as much as to the core figures beneath it. The sense that a challenge reading names a real, recurring obstacle is also the kind of effect the psychologist Bertram Forer demonstrated in 1948, when identical, deliberately vague personality sketches handed to thirty-nine students were rated, on average, better than four out of five for personal accuracy, a result skeptics cite as the likely explanation for why the Main Challenge this figure feeds feels specifically true.