This reminded me of my school days. We used it so frequently.Its like saying 'let's hope for a good outcome'.👍🏼
Significance of crossing one's fingers :
The gesture of crossing one's fingers for good luck is older than one might think: in some pre-Christian European cultures, two people would cross their fingers together as a show of support, teamwork, or mutual well-wishing: very much like the modern handshake.

The medieval Christians adapted it as a variation on the sign of the cross, to ward off witches and evil spirits (in the same way that today's crosses can supposedly keep vampires at bay). 😈
Over the centuries, 'keeping away the bad' evolved into 'inviting forth the good', and thus was the modern meaning of the superstition born.
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