The Evan Marshall Stopping Power books and Massad Ayoob's columns are based on real life experiences and feedback. This makes them more useful than any theories (including theirs). They make for interesting and informative reading.
Skill can accomplish marvelous things with less than perfect tools. Wild Bill Hickock did just fine with a single-action .36 Colt Navy, which is roughly equivalent to a full-sized .380.
Some of the most important things about a defensive handgun are:
1. It must be concealable.
2. It must be comfortable for you to carry at all times.
3. It must use your shooting skills well (i.e., it must point naturally and quickly, have a good trigger, and shoot to point of aim for you).
4. It is the most effective caliber and bullet choice meeting these criteria.
5. There are not a lot of levers and safeties that have to be pushed to make the gun work (i.e., all you have to do is point and pull trigger). [Murphy is alive and well.]
The truth is that you will probably need several handguns to fully meet your self-defense needs in differing circumstances.