The inner itch to “just do it” is the artist’s compass.
Although as artists we make maps, we seldom find them. An artistic career does not resemble the linear step-by-step climb of a banker’s career trajectory. Art is not linear, and neither is the artist’s life. There are no certain routes. You do not become a novelist by moving from A to B to C.
Julia Cameron, Walking in this World
The reward is in the making of the thing. Do it for that.
Nora Bonner 
I think these artist/non-artists distinctions diminish our human predicament a bit. Many careers and lives are “non-linear,” and I think on some level or another everyone has to to eke out a path through uncertainty. Perhaps, considering careers alone, some are fairly “linear,” but there’s a lot more to a life than a career, and even a career has many dimensions.
I think Julia Cameron would agree with you that there is more to life than career. Also, this passage is taken out of context from her greater work, which is to encourage everyone to make art and embrace creativity, whether or not it becomes a “career”. Even so, it seems there is a special place in her heart for anyone who sacrifices comforts in order to make art, and she does encourage such sacrifices in her writing. I nonetheless think she would call a person who creates, on any level, an artist; she encourages gardening and baking as creative work, for instance.
That said, this blog is where I record my thoughts about being a writer (“anyone who writes”), my own writing, and being a part of the literary community. Cameron’s words about the non-linear career path resonated with me in context of that literary community, where we often fool ourselves into thinking that there is a linear path: we publish short stories in journals, an agent finds us and helps us land a two-book contract for us to publish our short story collections alongside our first, pending, novels, which go on to win awards and help us land tenure-track positions at a major university, the second novel, the third, etc. Such thinking does exist, fiercely, and I think writers need to protect their work from this mindset. The writers who focus more on what they hope to get out of their writing will probably end up quitting, because there is no promise of pay off. To be a writer is to accept the work on average brings in $0-150 dollars a year; it requires a persistence, a willingness to continue revising a story after it has been rejected from 20 places, sometimes more, until it finds a home.
I liked this passage because it reminded me to just do the writing and not worry about the milestones; that writing is the thing, and the rest is consequence of the writing. Most writers I know need to hear that. If the words apply to other walks of life, that is great.