I had a boss years ago who would encourage me, whenever I was interested in e.g. a new library or framework, to go and reinvent the wheel in my spare time i.e. build it myself from scratch first to understand what the problems it solves actually are.
I've never built my own anything quite as low level as the build-your-own.org projects, but doing things like implementing a PHP web server with a class loader without any frameworks, or a JS templating system which stores the state of the UI in a big ol' object and updates the DOM automatically, has given me the deeper understanding of these things that I've later needed to debug weird issues and find creative fixes.
I had a boss years ago who would encourage me, whenever I was interested in e.g. a new library or framework, to go and reinvent the wheel in my spare time i.e. build it myself from scratch first to understand what the problems it solves actually are.
I've never built my own anything quite as low level as the build-your-own.org projects, but doing things like implementing a PHP web server with a class loader without any frameworks, or a JS templating system which stores the state of the UI in a big ol' object and updates the DOM automatically, has given me the deeper understanding of these things that I've later needed to debug weird issues and find creative fixes.