Not even doing it from scratch is the hard thing, the hard thing is getting the experience to know how to fit stuff together the best way to achieve your design and utilitarian goals, what wood to use, etc.

The hard thing isn’t building the date parsing library in assembly, it’s learning assembly well enough to do it in the first place.

I’m not sure where this discussion began but I was rebelling against everyone who says “just buy it” in regards to anything hard to do.