At my work I try to build everything from scratch but my boss hates it.

Also sometimes known as “not invented here syndrome”.

Sometimes it’s useful to know how something works and to be easily able to change every piece of the stack, other times it’s a massive waste of time and the end result is a worse documented and worse developed solution than what hundreds if not thousands of people have built and tested over the years.

Depends on what you’re working on, really, I’ve seen some really unfortunate stuff once people start rolling their own security stuff and it’s not like you can ask StackOverflow about why some random bespoke library or framework is full of weird behaviour.

But for personal learning projects? Go wild!

as he probably should. but building everything from scratch just is the autistic urge to actually understand what you're doing. not implying you're autistic or anything, but I am and I can't always stop myself from doing the same thing, hehe.

Your boss will hate it much more when the React-Tailwind-DaisyUI-datatable that imports 150 other npm packages becomes a massive security liability

Well yeah, don't USE your janky from-scratch libraries at work of there's something written & maintained by a bigger team. It's a learning exercise.

Yah lol, agreed