I do spread myself thin, in some ways.
I guess it depends on how you define "master." If it is relation to the subject material, there is always more to know when it comes to anything interesting, so it is hard to "master," particularly if your reference point is perfection. And I suspect INTJs are more aware of their deficiencies in this area than some other types - though not all of us care to admit it publicly. If it is in relation to other people and their level of knowledge, well that's easy if you're keen, but what INTJ defines their knowledgebase in relation to other people?
I guess it depends on how you define "master." If it is relation to the subject material, there is always more to know when it comes to anything interesting, so it is hard to "master," particularly if your reference point is perfection. And I suspect INTJs are more aware of their deficiencies in this area than some other types - though not all of us care to admit it publicly. If it is in relation to other people and their level of knowledge, well that's easy if you're keen, but what INTJ defines their knowledgebase in relation to other people?