I am continually amazed at those people who go to the trouble of getting a concealed-carry permit and professional training, but still don't carry their self-defense gun 24/7. They offer explanations, such as they just want to have a gun for protection in their car. Some also think carrying a gun all the time is a bit paranoid. These arguments seem to boil down to the notion that they just want to have their handgun around if they "need" it.
The fact is, a handgun, any handgun, is a poor choice for personal defense. Pistols and revolvers tend to lack the power often needed to stop a criminal attack instantly. If a person knew he was going to have to fight for his life, choosing a rifle or shotgun makes far more sense. The trouble is rifles and shotguns are difficult to conceal and somewhat bothersome to try to carry on your person every day. The value of the handgun is its portability.
In reality, we don't know when we might need a defensive firearm. Criminal attacks don't come on schedule and can't be predicted. Violent criminals often plan their attacks very carefully, and they look for the moment when they will have the best chance of succeeding in their assault. When their targets are lulled into a false sense of security, that's when they are the most vulnerable. And that is when criminals believe their intended victims are less likely to be able to resist.
When that attack occurs, it will almost always be with a swiftness that doesn't give much advanced warning. The honest citizen will very likely not have the time to go back into the house for his defensive handgun, nor to his car, even if it is parked nearby. In the face of most violent criminal attacks, the citizen has only seconds in which he can effectively react. Consider the Gunfight at the OK Corral was over in about 30 seconds. And in that 30 seconds, some 30 shots were fired.
A far more realistic approach to personal defense is to be alert and armed. Since no one can effectively predict when an attack will occur, the best approach is to be armed all the time (where legal). Col. Jeff Cooper once said, "If you are reading this and can't put your hand on a defensive firearm, all of your planning and training has been wasted."