To move sharply into an exact position. Snapping removes the in-between so nothing lands slightly wrong.
Middle Low German / Middle Dutch snappen (to seize, to snatch), likely imitative of the sound of a sudden crack; motion that removes every in-between so nothing lands slightly wrong.
A commitment made all at once rather than eased into — the suddenness is what buys the certainty, since anything that arrives gradually can also drift gradually.