Remember the scene near the end of It's a Wonderful Life, where Jimmy Stewart, playing the role of George Bailey, breaks down in a pub, crying out to God in utter despair? (Watch the scene here; fast-forward to the 5:30 mark.)
Apparently Stewart wasn't really acting; those tears were real.
In this 1977 article that Stewart wrote for Guideposts, the actor recalls that George "is unaware that most of the people in town are arduously praying for him. In this scene, at the lowest point in George Bailey's life, Frank Capra was shooting a long shot of me slumped in despair. In agony I raise my eyes and following the script, plead, 'God...God...dear Father in heaven, I'm not a praying man, but if You're up there and You can hear me, show me the way, I'm at the end of my rope. Show me the way, God...'
"As I said those words, I felt the loneliness and hopelessness of people who had nowhere to turn, and my eyes filled with tears. I broke down sobbing. This was not planned at all, but the power of that ...1