The following video was produced by the city of Houston, Texas and the Department of Homeland Security as a training aid to inform citizens of how to react and what to do to survive an active shooting incident like we have seen lately. While there is some excellent advice, depending on the exact situation a person my find themselves in and of course, the location, they do not mention getting the proper training on the use of a firearm, arming yourself and being prepared to use it if need be.
It is unlikely that any of us would ever be faced with such a situation, but not as unlikely as it once was. It could happen in a location where you cannot run, cannot hide or do not have anything to improvise as a weapon to defend yourself. Buying a gun alone is not good enough. You must be trained, maintain proficiency and be prepared to take a life. If not, you should not arm yourself.
Read more as well a version in Spanish here