[smt88]

"To use a library effectively, you have to be able to write it."

That's a blanket statement. If we find one exception to this rule, then we can say that it's 100% false (since its truthfulness is binary -- it's either true or false).

To find one exception, we only need to find a single "good" piece of software whose author can't write 100% of the dependencies, including: (probably) C/C++ compilers, FS drivers, low-level network libraries, and the widely-used monster that is SSH.

[awinter-py]

You're not 100% wrong but you chose the wrong examples.

Compilers & drivers aren't libraries. Low-level network libraries, using libuv as an example, have concurrency gotchas that require awareness on the part of the app developer. Using TCP as an example, think of the pain people go through over nagling.

Security software is the best example of something we use without understanding but it has gotchas; you need a nontrivial understanding of the internals to guard against sidechannel attacks.

[dalke]

"Compilers & drivers aren't libraries"? I've used LLVM as a library to just-in-time compile from Python. How is that not a library?

BTW, I've used primality testers I don't understand and couldn't implement on my own. How might I be more effective in calling is_prime()?