Realistically, one can never fully master a martial art. There is always room for improvement. However, with a good understanding of the essential aspects of the art and, most importantly, a functional ability to apply it in a practical means, one may rightfully claim a level of mastery. This is defined as comprehensive knowledge or command of the skill. To achieve a masters rank may be likened to earning a masters degree in academic schooling. It does not mean one is the best at something, but it should indicate what may be deemed an expert level of accomplishment.
Do not become overly concerned with whether or not you can master a total martial art. It is better to focus on developing and maintaining even a limited set of martial skills. During a confrontation, your opponent will not have any concern for what formalities you may have missed from your chosen style.
You may well be able to stop all opponents with a very limited knowledge of a system. It takes only one good shot to end a fight. Prize fighters often gain a reputation for one or two strong attributes, around which they build their entire career.
The basic skills form the foundation from which you execute all techniques. Martial artists fail at fighting when they lack one or more of the basic skills. They lack conditioning. This is not only the hardening of the anatomical weapons, but also encompasses flexibility, muscular development, balance, movement, speed, timing, an so on.
These skills, or attributes, require constant development and refining if they are to be maintained. People mistakenly claim to know martial arts. This is relevant in a teaching capacity, but the intended implication is that knowing martial arts equates to competent self-defense ability. Knowledge alone is not sufficient without active training. Understanding how to kick and punch is of limited use unless the body can meet the demands of application.
Certain skills, are emphasized more or less, depending on the particular approach to fighting. When it comes to striking systems, damaging force is the requirement, yet it is this very force that most would-be strikers lack. Very often, these practitioners actually manage to land some of their blows. The problem is, the strikes fail to stop the opponent.
There is debate regarding the need for exceptional power when pressure points are struck, but realistically, most practitioners will not be able to strike such targets accurately in a live scenario. Even under ideal circumstances, pressure points which may be painful when manipulated in the dojo, will not necessarily be effective against an enraged attacker. One can theorize indefinitely, but theory must be tested through experimentation.
If you discover that you actually can reliably incapacitate opponents with pressure point attacks, then you have a rare ability. If not, you might consider conditioning yourself to generate real knockdown power.