Actually, experimental psychology and neuroscience - you're quite funny. I'm getting my PhD currently, and I can tell someone has an insecurity problem since you feel the need to disparage me behind your keyboard. I also research linguistics fyi, so I'd really like a single opinion from you on this topic matter. Where exactly is the "nothingness"? Have you yourself actually considered there are a great deal of linguistic uncertainties to be hashed out between monolinguals and bilinguals? If you actually think what I wrote is just filler then you can't even see the point and that's just rich. Maybe don't disparage someone for the way they speak, I approached this topic raising a different and new perspective and it's people like you who make earnest discussion impossible.

I think it's quite dangerous how we can place ourself in pitfalls solely because the decision is in the eye of the beholder. If language acquisition (like another commenter rightfully said) were remotely the same as other processes, maybe the comparisons would be more apt. However, what exactly is wrong with making errors in the target language? Consider conversely this, is there actually a need for someone to arguably overlearn a language to a point (like many of us here) that we not only take for granted, but possibly entrap ourselves within a sociolinguistic framework?

The idea that we cannot learn a second language past 2x can be disproven, if there is evidence for it - there is no law here. More importantly, as that is not an interesting question - why might it be the case that we can't? To be frank, it might just be because you are telling yourself the lie that you couldn't, because of the investment you've made in your native language.

"Errors" in a second language are arguably not always such a bad thing - yes, communication is important but does overlearning one language prevent us from making more progress in others? Also, if we stop considering errors to be a bad thing, then we face the potential reality that novelty is present everywhere in second-language learning, but when speaking your native language the experience of novelty (in relation to the language) is nigh inexperienced. Except, in many cases, when someone speaks "improperly" or wrongly.

We cannot as a culture distinguish ourselves from the desire for everyone to be like us, and/or for ourselves to be like everyone. Of course someone will come along and disagree, but my point on that note is that perhaps the significance of the errors we attach related to language is simply code for our disdain for something else.