While I agree with this idealistically and wish that all the code I've come across adhered to published interfaces, unfortunately that hasn't been the case.

Published interfaces may also not be possible in certain code bases or frameworks -- think of a Chef recipe for instance where most (ruby) code is being written to directly interact with the system rather than provide a service to other parts of the system. Dynamically generating variable names and key/value pairs in Chef recipes is a common pattern I've seen which makes grepping and isolating issues difficult if not impossible.

That's sufficient when the code is flawless and you never have to look at it. I.e. pretty much never.

The rest of the time it is still a huge benefit to be able to easily navigate the source. And frankly, a lot of the time the source is a more concise source of truth than decently written documentation.

Also, a working and redundant interface wins over a buggy, broken, and concise interface.

But I don't think the OP argued against either documentation or fixing bugs, so I fear that both of our comments are irrelevant.

Well said. Too bad most coders are horrible are finalizing an interface.

Agreed. The answer to this is documentation; not dogma.