Postel's law

As defined by Jon Postel in RFC 793
https://tools.ietf.org/html/rfc793
TCP implementations will follow a general principle of robustness:  be
conservative in what you do, be liberal in what you accept from others.

#harmful
Postel's law considered harmful

Being conservative in what you do disincentivizes people from
being liberal in what they accept.
+
Being liberal in what you accept disincentivizes people from being
conservative in what they do.

This is not my idea,

Martin Thompson wrote
https://tools.ietf.org/html/draft-iab-protocol-maintenance-04
A flaw can become entrenched as a de facto standard. Any implementation
of the protocol is required to replicate the aberrant behavior,
or it is not interoperable. This is both a consequence of applying
the robustness principle, and a product of a natural reluctance
to avoid fatal error conditions.  Ensuring interoperability in
this environment is often referred to as aiming to be "bug for
bug compatible".

Postel's Law again https://blog.dshr.org/2017/02/postels-law-again.html
Postel's Law has 2 parts http://essaysfromexodus.scripting.com/postelsLaw
Robustness Principle Reconsidered https://queue.acm.org/detail.cfm?id=1999945