I think the gist of it is that JavaScript doesn't have threads, or isolated state. So your code can theoretically do anything it wants, but the React concurrenc

I think the gist of it is that JavaScript doesn't have threads, or isolated state. So your code can theoretically do anything it wants, but the React concurrency stuff is riding on your code only using a specific set of APIs, and does things like calling your functions on cloned instances with different props. If you aren't writing your code "in the React way" it very quickly leads to very confusing inconsistent behaviors.