It is the nature of filmmaking that scenes must be extensively planned before cameras can roll. However, planning things down to the last detail can discourage improvisation and experimentation; what filmmakers sometimes call catching “lightening in the bottle.”
Below is a nice collection of famous scenes that for various reasons were unscripted. From “Here’s looking at you Kid” to “Leave the gun, take the cannoli” these moments are a nice reminder that sometimes the filmmaking gods reward living in the moment.