Why does the alignment relative to a prior point matter? e.g. A small snowball could be nearly perfectly enmeshed with the surrounding snow on top of a steep h

Why does the alignment relative to a prior point matter? e.g. A small snowball could be nearly perfectly enmeshed with the surrounding snow on top of a steep hill but that doesn’t stop the small snowball from rolling down the hill and becoming a very large snowball in a few seconds, and wrecking some unfortunate passer-by at the bottom. A few microns of freezing rain may have been the deciding factor so even a 99.9% relative ‘alignment’ between snowball and snowy hill top would still be irrelevant for the unlucky person. Who may have walked by 10000 times prior.