On the one hand, forgetting or confusing the words of the Lord's Prayer (the "Our Father") used to be proof that you were consorting with the devil. It could get you executed.
On the other hand, there is a charming Russian story about a holy hermit (a staretz) who lived on an island, praying all day.
The local Bishop was alarmed that the hermit was not versed in traditional prayers of the Church, so he chartered a boat to the island. He taught the hermit the Lord's Prayer, which the humble and obedient staretz promised to pray.
As the Bishop was about halfway back to the mainland, he heard a voice and turned around to see the staretz, running across the water and shouting, "Bishop! Wait! I forgot a line of the prayer!"
Today I took Communion to a lady in a nursing facility. We were praying the Lord's Prayer together and she suddenly stopped - I don't remember at which point. I finished the prayer and paused to make sure she was still connected to what we were doing.
She spoke up as if continuing the prayer, "And Lord...", then offered an extended, extemporaneous intercession for the well being and mission of our parish and for God's assistance to any members who might be struggling with problems.
I wonder if she ever got cold toes while running across a lake.