It's a bit simpler than that.
There are all kinds of strategies and techniques geniuses use--the same way a woodworker uses a rotary router upon wood--to achieve maximum utility from their brain. It is a simple tool requiring skill to produce results, as you apply skill with e.g. Krita to draw a digital painting: one tool, hundreds of technical procedures to produce complex results.
One of the most primary strategies used by the greatest geniuses--not simply experts who excel in a single field of interest, but geniuses who excel at anything they attempt on a dare--is to instill motivation. They examine a problem requiring effort, understand its implications, and find a reason for interest: something they already want, or a new thing they suddenly realize a desire for, is more readily achieved by this new effort. In this way, every task, every study, every problem becomes engrossing; the individual has an unfettered desire to pursue this thing which is lain before him, and so fails to recognize the effort he puts forth, and so puts forth much effort without resistance, and so excels.
You observe simply that some things require excessive effort to gain an end not sufficiently interesting; were that end more interesting, it would be more pursued. Likewise, the closer that effort is to something interesting--if an aspect of the effort itself is discovered interesting, or if each step of progression directly translates to a useful step of progression in something else interesting--the more strongly it is pursued. Simply put: if upon completion of X you can improve Y, completing X becomes interesting because of Y; if by way of progressing toward completion of X you improve Y, X becomes interesting because it is essentially Y as well.
You observe, of course, that turning the second situation into the first is a good control for humans: if doing 10% of X grants you 10% of Y, and you do not want people interested in Y to perform X, then you must adjust the system surrounding X, Y, or both such that completing X grants Y, or such that X has less impact on Y, so as to require more effort for returns and less returns for effort.