They are unable to jettison the mental residue from pondering Possibility 1 before they turn their minds to Possibility 2. That means the possiblities have a CUMULATIVE EFFECT in their minds, so that a subjective PROBABILITY THRESHOLD is soon reached, and they interpret a dozen possibles (improbabilities) as a cumulative probability.
They can't seem to grasp that most observations are independent of each other, i.e. one possibility doesn't make the second possiblity any more likely.
Zero times 12 equals zero, not 12.