C++ has a proposal process for changes to the language and standard library (see also the ISO C++ wiki's page on "How To Submit a Proposal", the Std Proposals mailing list, the list of Standards Committee papers, and the papers repo on the cplusplus GitHub organization).

Programming-language design doesn't happen in a vacuum. For many language-building projects, there's a team of people working together- such as a committee (as is the case with C++).

For those who want to learn from a well-established language with a design committee- particularly from "mistakes" it may have made in terms of its culture surrounding design proposals, and how it is (potentially) learning from those mistakes,

What kinds of problems (and associated solutions / goals to strive for) have C++ committee members historically identified with their proposal culture?

Please either quote or paraphrase, but in either case, link also to the source.