django1993

A startup that keeps eating more and more money like a blackhole without emitting a single penny of profit.

I would also recommend reading Computer Systems: A Programmer's Perspective, 3rd Edition.

+1 for OSTEP

The name of the blog is 'writepay', which should give a hint.

Maybe because structs have some fields private and some public. To add a method outside the package would be to make those private fields visible in the method outside the package which then allows such methods to manipulate the struct and that will break the abstraction provided by it.