From the OP:
> When I say “run” I don’t just mean executing a program; I mean operating it in production, with all that it entails: deploying, upgrading, observing, auditing, monitoring, fixing, decommissioning, etc. As Dan McKinley puts it: "It is basically always the case that the long-term costs of keeping a system working reliably vastly exceed any inconveniences you encounter while building it."
One of the things separating a great developer from a good one, IMO, is the ability to treat the documented API boundary of an open-source library as something that isn't sacrosanct and impenetrable.
How comfortable are you with command-clicking into, or outright cloning and reading, a library's source to understand the nuance that the documentation may not convey (or situation where the documentation is outright wrong)? Depending on your language's support for it, have you monkey-patched issues, or forked a library (and ideally submitted patches upstream) to add extension points you might need? Are you used to setting breakpoints inside of libraries, not just your own code, so you can understand how data is represented internally when debugging?
And when you're evaluating whether to use a library in the first place, do you just look at the API and examples, or do you read the source to understand whether the underlying code prioritized maintainability, extensibility, and test coverage? Do you read changelogs and think about whether the library maintainers prioritize your ability to upgrade without breaking even your patched/forked code?
The brilliance of open source is that we can do this. We're not just fitting gears together - we're able to fabricate iterations on those gears as we need to.