I definitely think the error could be improved but I'm not sure it should really say "just shove it in an `Arc<Mutex>`," because that really is only sometimes the right solution and it might lead people to make poor choices by default.
I think a lot of the problem is really with the confusingness of the concept of static lifetime in rust to begin with, where it's kinda used for both "lives forever" and "doesn't reference anything that lives longer than it"[1]. I hope someday these meanings get different names, tbh.
But when you see that error the naive thought is like... "ok better make it live forever" but it really just means you need to make it something that you control, and there are other ways to do that than a refcounting mutex.
