Remembering and referencing Maslow's Hierarchy of Needs just now ... this is the top of the pyramid - Self Actualization - achieving full potential including creative activities. Maybe this vision/desire becomes more prevalent in SW Engineers (in US at least) in their 30's or 40's because you've got the bottom tiers completed (I know its not like a video game skill tree) and possibly have Esteem met with being accomplished in comparison to many other careers. Tech is a sought after field, known to have high income and requires a certain mindset to be good at it. Being good, not even great, at Tech in the US gets you thru the bottom 4 pretty well.
If your job lacks any avenue towards creativity or path towards self-actualization professionally (like being "known" in tech, building a widely used thing, writing a tech book, etc.) then you seek out other avenues towards self-actualization.
My problem is having these ideas of things that I want to do, like an idea for a novel as an example, but not knowing how/where to start or just plain ignoring the sheer amount of work that is required and day-dreaming about it. That's not at the top of my list but that idea keeps percolating up at times. I like your approach about writing down a plan to fulfill those self-actualization types of things.
An example where I've realized its a lot more work is building a desk top out of walnut for a sit/stand desk. From roughly cut boards to a finished top looks easy on youtube videos. Squaring a board to join with other boards without pro tools is a lot of work. So much work, much more than I thought. Some of the work is part of the process of learning.