Not everything has to be a life-improving challenge - sometimes you just want to ship some code!

I would say shipping is definitely life improving. Shipping is where you expose your work to the public and open it up to feedback and criticism. You can learn a lot more from direct feedback than you can learn from a general book.

I have far too many books and half finished projects that will never get finished. I have forgotten most of the stuff I learned from them.

Sure! But if the daily coding is predicated on a sense that, "this is how one becomes great" it is not sufficient for that goal.

It's easy to become complacent. Most people are.