There was once a programmer who was attached to the court of the warlord of Wu.

There was once a programmer who was attached to the court of the
warlord of Wu. The warlord asked the programmer: "Which is easier to design:
an accounting package or an operating system?"
"An operating system," replied the programmer.
The warlord uttered an exclamation of disbelief. "Surely an
accounting package is trivial next to the complexity of an operating
system," he said.
"Not so," said the programmer, "when designing an accounting package,
the programmer operates as a mediator between people having different ideas:
how it must operate, how its reports must appear, and how it must conform to
the tax laws. By contrast, an operating system is not limited my outside
appearances. When designing an operating system, the programmer seeks the
simplest harmony between machine and ideas. This is why an operating system
is easier to design."
The warlord of Wu nodded and smiled. "That is all good and well, but
which is easier to debug?"
The programmer made no reply.
-- Geoffrey James, "The Tao of Programming"