I don’t think it was ever common for people to literally use the phrase “steadfast friends”. The word “fast” by itself meant (and still means sometimes) something like steady or firmly stuck. So “fast friends” per se was always a perfectly fine phrase. It hasn’t been shortened from some other form.

People trying to explain the origin of the phrase “fast friends” point to the word “steadfast” as an example of where this sense of fast persists. You might also notice the same meaning in our words fasten, colorfast, etc.

So, my argument was it was a root, not a commonly used word. I was wrong anyway so it's irrelevant.

Having actually looked in to this now with a bit more detail than "google it to check your understanding and look at the first result":

It appears you're right, and "fast" is derived from faest while steadfast is a combination of steade and... fast.

Fast friends is a perfectly cromulent phrase :)

BTW, the person you originally replied to used "fast" as in "quickly," as in the title of this submission.

The "fast friends" etymological discussion is a non sequitur.

That's true.

I'm still outraged that anyone would want to force a so-called friend to abstain from nutrition.

So, and this is honest curiosity re. understanding the HN mindset... why did you go on that tangent when the only thing it shared with the comment you replied to was words in common?

I really, really quickly skimmed the comments and title then mentally chose the wrong order of "friend/fast/fast/friend".

The flaw in this particular part of the HN mindset is looking at a set of information and thinking you can instantly identify the other person's problem (or that there is one!) and explain/solve it using what you already know.

I think other people might recognize this in their own thinking sometimes too!

I think that's fine, as long as you learn to back down and reconsider the moment someone presents competing information.