The Greek drinking custom of pouring the third libation to Zeus Soter, origin of the proverb the third time is lucky.
Documented
The libation sequence
The LSJ entry shown in the screenshot records it: the third cup of wine was dedicated to Zeus Soter, to triton to soteri. Plato cites the proverb in the Republic and Philebus; Aeschylus's Oresteia trilogy itself plays the pattern, the third play delivers rescue. The custom anchored luck to the savior's cup.
Assessment: Documented: Plato, the dramatists, and the lexicon all attest the sequence.
Stories
The surviving superstition
Third time lucky, third time's the charm: English proverbs with no remembered libation underneath. The toast died; the count survived; nobody at the pub knows they are counting cups to Zeus.
Assessment: Stories: the proverb lineage is plausible and disputed; some folklorists derive the English charm independently.
Interesting claims
Three as the delivery number
The pattern numerologists notice and classicists tolerate: the third attempt as the saved one runs through Greek drama structure, fairy tales, and sports. Soter attached to the ordinal made luck a theology: the rescuer arrives on three.
Assessment: Interesting: cross-cultural threes are documented; the Zeus wiring is one thread of many.
Sources and further reading
Liddell-Scott-Jones, 'soter' sense 2, the third libation