It becomes important in the further consideration of coincidences
to emphasize the great opportunity presented in their description
for error, for defective observation, for neglect of details,
for exaggeration of the degree of correspondence; and equally
demonstrable is the slight amount of such error or mal-observation
that is all-sufficient to convert a plain fact into a mystery.
Consider the disfigurement that a simple tale undergoes as it passes
from mouth to mouth; the forgetfulness of important details and the
introduction of imaginary ones, exhibited upon the witness stand; the
almost universal tendency to substitute inferences from sensations
and observations for the actual occurrences; and add to these the
striking results of experimental inquiry in this direction--for
example, the divergences between the accounts of sleight-of-hand
performances or spiritualistic séances and what really occurred--and
it becomes less difficult to understand why we so often fail to
apply general principles to individual cases. The cases cannot be
explained as they are recorded, because as recorded they do not
furnish the essential points upon which the explanation hinges. The
narrator may be confident that the points of the story are correctly
observed, that all the details are given; and yet this feeling of
confidence is by no means to be trusted. It is quite possible that
the points that would shed most light on the problem are too trivial
to attract attention; a slightly imperfect connection as effectively
breaks the circuit and cuts off the possibility of illumination as
a more serious disturbance. After the explanation is given or the
gap supplied or the break discovered, we often wonder how we could
have failed to detect the source of the mystery; but before we know
what to observe and what to record and what to be on our guard
against, the possibility of error is extremely great, far greater
than most of us would be willing to make allowance for; and the
strict demonstration as also the refutation of a proposed explanation
becomes correspondingly difficult.