In the movies one often sees the bad guy with his gun to a hostage's head. Depending on the intended outcome, the hero either puts down and wins later, or shoots the criminal and wins immediately. 

I know that movies/TV etc has very little to do with real life, therefore I have questions for the experienced guys: 

1. How little/often does this occur in real life? Ie: is it even realistic to prep the brain for such a situation?

2. Is there anything one should keep in mind in preparation for such a situation? 

(For us here in SA, we would probably be facing a seasoned and hardened criminal, or a drug addict, or a combination of both.)