It is very hard to say the way you will react, even though if at gunpoint you should never react.
It is not safe to react, if possible remain calm and pray, pretty much.
Never react at funpoint or even when people use a knife on you, for example. Also having your own knife for protection can end up bad for you, after all the bad person might get it from your hands and use it against you.
I was robbed once, and I reacted to the person, even though he had no guns or knives, I noticed he had no gun but if he had a knife I could be dead right now. He hit me on the face and kicked me also...he pulled my bag and I fell backwards, I hurt my head, lost my glasses and broke a rib in the process.
Though my neighbours managed to get my bag back, I really never imagined reacting...but at the rush you end up doing things you would never imagine.