Actually NO, someone can be a Jack of all trades and Master of all!
For haven read somewhere on the Internet about a job description asking for “a Jack of all trades and a Master of some (or all if possible)”, I gave it some thoughts and ended-up modeling the (social) problem as an algorithmic problem as follows:
The human brain capacity likely has an upper limit, say B. Suppose that n trades each have an importance level of Ii where i ranges from 1 to n. Further suppose that for each trade i, a person’s brain has a difficulty level of Di for learning it, and has a mastery level of Mi representing how much of it the brain has learned. For that trade i this gives a brain-efficiency of Ei=Ii*Mi and a brain-consumption of Ci=Di*Mi. That said, the problem of maximising the total efficiency of the brain can be modeled as the problem of maximising the sum of all Ei subject to the constraint that the sum of all Ci is less than or equal to the brain-capacity B. This sum(C) is in fact the total amount of information contained in the brain.
Given integer values for the single number B and the vectors I and D, the optimisation problem of finding the vector M such that sum(E) is maximised, subject to the constraint that sum(C)<=B, is essentially the well-known Knapsack Problem. It can be solved efficiently using a Dynamic Programming algorithm. If M is not restricted to integer values then the Simplex Method can be used instead. The obtained result M can then be used to judge the amount of time and effort to spend in mastering each of the different n trades.
Full mastery of all (relevant) trades is not possible due to the brain capacity constraint. The ideal attribute is the ability to surpass one’s limit thereby increasing one’s capacity. But doing this is hardly possible if ever possible at all. What I personally do is train my ability to adapt my mastery levels to changes in importance levels. Thus with my limited brain capacity, I find myself significantly forgetting one knowledge for the sake of another of higher importance. However I nicely document the old knowledge in order to easily remember it later when I need it again. This way I give the impression that I am both a jack of all trades and a master of all!
That said, I believe the ability to adapt is the trade with highest importance that governs all others. Also it has a very low associated difficulty, although this may just be an innate feature to some people?!