Scry is a clipped form of descry, from Old French descrier, to proclaim, then to catch sight of, ultimately from Latin describere's kin. English crystallomancy and catoptromancy (mirror-divination) are the technical names; the practice is attested from classical Greece to Dee's 1580s sessions with Edward Kelley and the shew-stone.
The behavioral observation: gaze at any featureless dark surface long enough, water, obsidian, a locked phone, and the visual cortex begins supplying content. The hypnagogic theater does the rest; the ancients called the projector an angel.
The root's irony: descry began as proclaim, to cry out what is seen. The scryer does not merely see; the scryer publishes. Every divination is a press release from a mirror, which explains both the confidence and the error rate.
Is the mirror showing the future, or is the future what gazers always see in mirrors?