Doing one thing well is over, isn’t it? After all, the portfolio career is what many strive for, notwithstanding those who might actually crave one job, one role, one career, but for the sake of necessity (i.e being able to support themselves financially) are obligated to have three or four, or five jobs instead.
Having one job is very last century, just as having a job was so last century before that, and even companies have moved away from that. After all, Microsoft bought Skype, Apple bought Beats, Facebook bought Instagram, and Amazon sells, well, everything. And so hobbies can become cash cows, a pet project might become your pension: everything is up for grabs. And why not? We lead much more diverse life experiences than our antecedents.
If there is an evolutionary explanation for why doing one thing well might be over, where then does that leave the 10,000 hours brigade and and their advocacy of time spent grafting (or crafting) as a benchmark of excellence? Looking around, anecdotally, 'good enough', with its promotion of busyness over brilliance, is perhaps the best one can expect from a landscape in which TL;DR is often a default position. However, what’s good enough today probably won’t be good enough next month, and since we only really know what good enough is until someone tells us what it isn’t, making sure you do one thing, your core thing (whatever that is) really, really well is unlikely to do any harm in the foreseeable future. Best to keep in mind that is by no means the be all and end all, though.