Not really relevant to the topic of open source insulin, but insulin is sometimes administered intravenously in a hospital setting as an emergency measure to control potentially-fatal levels of hyperglycemia.
Not just as an emergency measure; if you've got IVs set up anyway (e.g. because you're treating hypokalemia) then it may be more convenient to drip insulin in rather than administering it subcutaneously.
What i struggle the most when coming to a new language is the tooling that comes with it.
And how do I structure my code in this new language. Sure some things are universal, but some things are just hard to find out.
The js ecosystem is an especially tough example for this.