The more experienced I get, the more I've started to think that most of the 'principals', 'patterns' and 'best practices' tossed around in the industry are mostly bullshit.

Be attentive to the classes of bugs you (and your team) produce, and act accordingly to correct those.

Being liberal in what you accept is fine, as long as what you accept is precisely documented. But then, is that actually "being liberal"?

Better advice is to not do something unexpected -- even if that unexpected result is clearly documented, but someone did not read it.

I disagree with the robustness principle. Be strict in what you accept - require them to meet the spec.

I think it's been a commonly held opinion in security circles for at least 15+ years that the Robustness principle is generally counterproductive to security. It (almost inevitably) leads to unexpected interactions between different systems which, ultimately, allow for Weird Machines to be constructed.

An argument can be made that it was instrumental in bootstrapping the early Internet, but it's not really necessary these days. People should know what they're doing 35+ years on.

It is usually better to just state fully formally up front what is acceptable and reject anything else out of hand. Of course some stuff does need dynamic checks, e.g. ACLs and such, but that's fine... rejecting "iffy" input before we get to that stage doesn't interfere with that.