A similar theory is used to explain cognitive biases, that when faced with a lot of information that is competing for our attention and mental energy and may also appear contradictory on the surface, our brain forms "short-cuts" that lead to cognitive biases, to filter out new or conflicting data. The problems with this are pretty obvious. Evolution has geared us toward survival, but not necessarily towards rationality or common sense.
Anyhow, this is one reason I do not think sticking to a few resources or the same kind of approach with language learning is not a good idea for the long run. Most beginner materials are typically designed to be narrow in scope because too much info too soon is understandably overwhelming, and that's OK as a starting point. But that can also get a learner stuck in that "narrow" mode if they are not conscious of it and make efforts to grow beyond it. This is, in my opinion, a good part of the whole "getting from B2 to C1" problem I've seen a lot of people discussing around here. Whether learners are conscious of it or not, they can grew accustomed to resources that keep the introduction of new information narrow and limited, and the learner can end up preferring that, making the transition to native materials more stressful and frustrating, simply because they have yet to develop the skills to cope with being giving a ton of information at once, like being able to intuitively process smaller units of language, like phatic expressions or little words such as articles, particles, prepositions and the like, or infer meaning of unfamiliar words from context--these skills in themselves are also mental short-cuts that we use with our native language all the time. I don't have any quick and simple solution to make this transition easier besides encouraging people to diversify their learning materials from the get-go, and to not shy away from using things like music, video games, TV, extensive reading, etc to broaden your experience of your TL outside of more traditional, more "controlled" methods of study that deliberately pace out the amount of information you encounter. You simply have to go out and embrace the chaos that is
language.
This also ties into my personal preference to make language learning enjoyable through using diverse media, like music and video games, because they encourage you mentally approach the language differently than you would with a textbook. You're getting your brain to experience the language from a different perspective, so your brain is much less likely to just zero in on what is familiar and comfortable and stay in that narrow focus the whole time. Plus, as a side note to this, research into the neuroscience of music has shown that when you sing, you are actually using a different part of your brain than when you are simply speaking. This is how I overcame my (very autistic) anxiety with speaking French--I learned a lot of French songs. I can sing about 3/4 of Zaz's first album by heart by now and also completely look like a clown speaking my wonky French in public without having a panic attack. Progress!
Singing a lot in French helped my brain to process the language via different pathways, so to get around my mental habit of hyperfocusing on things
I knew I often got wrong which, when I tried to speak, would trigger my anxiety.
As for PTSD, tangentially, I have found learning to process language at a more advanced level where I have to cope with receiving and grappling with a lot of information at once to be very helpful. PTSD's impact of brain and cognitive health is not fully understood, but we do know that stimulating the brain to develop more complex information-processing skills like learning a second language is profoundly beneficial. So language learning can be, essentially, a form of therapy for PTSD and I encourage anyone else who has PTSD to think of it like this and to keep your struggles with learning a new language in this more positive mindset--it may be hard, but learning itself is something that is healthy and good and can foster healing. But also, remember everyone progresses and heals at their own pace and with any other kind of therapy, the process can be slow and you'll have good days and bad days.
(Additionally, I am not at all suggesting that language learning or other learning for self-enrichment is a substitute for medical treatment. I've lived with PTSD for over 30 years so I've been through a lot in terms of managing and healing, including seeing a therapist and medication, and I do not expect anyone else compare themselves to me in terms of what they need to manage their PTSD. If your PTSD requires treatment such as medication or seeing a therapist to manage it, please do not think that language learning can replace that.)