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.