The basic idea of core activities is this—there are certain practices that we do most of our days. Take any of these activities out, and we find ourselves having a very different sort of day.
Nearly all of us have eating and sleeping as core activities. Of course, there are days with less eating, more sleeping, or the reverse, but for the most part, days will have some eating and some sleeping. Take away or increase eating or sleeping from a day, and the day becomes a different sort of day. We have words for those sorts of days: fasting/feasting and staying up/sleeping in, respectively.
Knowing that a person eats and sleeps doesn't isn't very informative. (Though knowing that a person doesn't may raise concern!) This is because we identify ourselves on more interesting things than just eating and sleeping. A person may, for instance, devote much time to researching eating and sleeping. Swimmers swim. Writers write. Programer program. Teachers teach. etc.
What do we call people that talk about maybe going to the gym? Or talk about possibly taking up painting one day? Or express a desire to learn another language? "Potential customers" may come to mind for those interested in selling goods/services. Usually, we don't refer to friends and family as "potential customers" though.
Here, I look in the mirror and ask myself—what are your core activities? If my job means writing, well, I better be writing everyday. If I would like to fancy myself as an artist, I better be getting myself to do art everyday. Actually making a plan to make sure a handful of things happen (near) daily leads to the inevitable conclusion—insofar as our interests are many, the opportunity costs for doing any one activity hit the feels. To do any one thing, we must forego doing an infinity of other things. But, indecision—for instance by refusing to commit to any one activity as a core activity—solves nothing. There too is an opportunity cost for indecision.
Likewise, postponing decision by choosing activities that take over our attention (i.e. seeking distractions) does little to directly solve the angst of failing to choose, failing to commit, and failing to execute.
Note to self: deliberately choose to do things, and do those things well. Doing things well that you didn't choose to do is a "good is the enemy of great". Focus is required. But so is direction—no shooting laser beams in rando directions 📡