Two problems: first is that casual association may be invisible to even hand-waving criteria; think good crypto PRNG output which is fully determined by seed and is serial number, but the parameters are practically unfittable from the data because the function is so chaotic. Second thing is that the more hand-waving you allow the more totally incidental relations will look "true". With a modern amounts of hypotheses, even Pearson correlation often becomes useless in this manner.