The belief that the third time something is attempted is more likely to succeed than the previous two attempts. It is also used as a good luck charm – spoken just before trying something for the third time.

The first time we come across what appears to be a precursor to this phrase is in Elizabeth Barrett Browning’s Letters addressed to R. H. Horne, 1839:

‘The luck of the third adventure’ is proverbial.

It is listed explicitly in Alexander Hislop’s The proverbs of Scotland, 1862:

“The third time’s lucky. “