Author Stephen Cox wrote in Saturday's Los Angeles Times that the powerful barroom scene in which Stewart's hero George Bailey tearfully prays for divine intervention was originally shot at too distant an angle.
The scene was emotionally draining for Stewart, who refused when director Frank Capra asked him to do it again.
In order to salvage the drama, Capra and his editing crew had to manually zoom the scene in frame by frame in order to catch the tears that had erupted from Stewart spontaneously.
The result was a tear-jerking chestnut that prompted "It's a Wonderful Life" to be rushed into release ahead of schedule in order to qualify for the 1946 Academy Awards where it received five nominations, including best actor and best picture.
Pregnant Mila Kunis wins 'Best Villain' at MTV Movie Awards
'Happy' fan videos make Pharrell cry [VIDEO]