Oh, come on, surely you know the answers to these. Nonetheless, I’ll humor you:

How does one know if another is mature enough to give truthful and honest feedback?

See how they provide feedback to/about other people. How accurate are they? Have they been proven wrong? What is their track record? If it’s consistently good, then that’s kind of a really strong voucher, no?

Furthermore, how does one discern if said feedback is actually truthful and honest?

Same as above; did you agree with their assessments of others based on the info you yourself have of those subjects? Can you verify that everything, or at least most of what, they said is correct? If they’re consistently exhibiting honesty, then why is there any reason to doubt it with you?

You neutrally build a case proving or disproving their maturity and trustworthiness. It’s almost scientific!

So, if what I say is stupid, a random anonymous stranger is more likely to tell me than a friend.

Ohhhhh. See, I was making a specific distinction between in-person strangers versus online strangers. In person is a lot trickier to get rude over, so I had meant that those such people will try to be polite and downplay stuff (on average, anyway; I know there are Karens). Contrast that with people online and, because we feel safe via the guise of anonymity, we’ll brutally say whatever the @#$% we want, hahaha!

However, I still think a mature friend in person is best. The friend you asked is not mature if they’re not giving an accurate portrayal of the situation (that they should already have had info on/the experience of).

Sorry, I had vaguely felt like my sentence back there could get misinterpreted after I typed it, but I didn’t know how to word it in any other way, so I had just proceeded. Haha.

I can’t know the unforeseen consequences of it.

This is… amazingly insightful (even though we should already know about this through all the time-travel dramedies we see, lol, but I guess I just forget to apply it to my own life regrets)… What a great neutralizer of negativity. Thanks for the reminder…

Well, now that borders on arrogance lol but I was going to say that that sure seemed like a healthy view, because there are certainly things I’d back and change if I could, even if it was mere exposure to certain ideas or my interpretation of them

Does that mean you absolutely love yourself in every way?

Go on…

“True, we’re really in preschool; let’s add more naps.” - Their leadership, probably

nobody knows me enough to not tell me my idea is stupid

What about the possibility that nobody here thinks your idea is stupid? I certainly don’t. I think feedback is extremely important and that this is a great question (which can only be solved by first having close, mature friends, and asking them).

One needs to talk with mature confidants, not just people who don’t know oneself well. They’ll be far likelier to tell you what’s up.