Here's the actual reason!
'Crossing the fingers' is a gesture of hand used by many people to wish for luck. Many people, mostly the children uses this gesture of hand to excuse their telling of a white lie. There have been different theories regarding the origin of finger-crossing for luck.
So have a look at this story to know the actual reason behind crossing the fingers.
It is believed that the 'crossed finger gesture' is a reference to the Christian religion used for wishing luck.
In early times, Christians were persecuted in the Roman empire and at that time they originated the 'fingers crossing' gesture which then became a secret way of showing the faith and recognizing fellow members.
Earlier, people used to cross their fingers with another person's fingers to show their trust and belief in each other.
Now people cross their fingers alone to wish them luck and seeking the support of God.
There are a few reasons for crossing the fingers but the main reason in the western world is to bring good luck or to show solidarity and support to someone else.
People used the 'cross finger sign' not just for wishing luck or God's favor but also to ward off evils and illness.
Crossing fingers is common among the soldiers during bloody battles, where soldiers needed a little luck and God's favor to see them through.
There are many people, especially the children, who cross their fingers just to excuse their lie.
People uses the 'cross finger gesture' while making a promise to invalidate the promise.