I've been strong-armed, by the deceivingly violent Steph, into rewriting my previous post in layman's terms.
Why do some people overuse their tertiary function? And why can loops/traps occur?
My first thought is, why do we interact at all? In general, we interact with each other to receive a desired response. I think that there are many types of responses. Desirable responses are preconceived, and there is a range of acceptable and unacceptable responses. For instance, if you tell someone you are sad, possible positive responses are empathy, advice, or a compliment. Possible negative responses are teasing, changing the subject, or an insult. Interactions are transactional like that.
If someone says something that came from using their top two functions and receives negative feedback, they may try using their first and third function. If their first and third functions produce positive responses, they may keep using it. The substitution happens naturally. Therefore you may think it is normal and arent aware you are even doing it. Prolonged exposure to this situation may even convince you that using your first and third functions is right and using your second function is wrong. So there is your loop.
Imagine my situation for a moment. A little Ti/Ne kid may make the observation that a baseball and basketball dropped at the same time from the same height hit the ground at the same time. After a few more observations the kid forms a theory

and is very happy with himself. He shares this thought with an adult and is expecting praise for his creative endeavors and reciprocated curiosity, but the all-knowing adult already knows about gravity. The all-knowing adult may even try to show their superiority by regurgitating the genius of someone else and demeaning your innovated thought

. And all the other little kids don't care to know about gravity until the all-knowing adult gives them a grade for it. (if someone says newton was an intj...... i will stick steph on you. newton is an intp to the max.)
In school they teach you 1+1=2. A Ti/Ne kid would think, "wtf are these shapes and why do they follow that pattern?

". All the other kids got it so the Ti/Ne kid must be stupid. The switch to Ti/Si just memorizes the pattern and moves on.... So on and so forth until something different happens. How long could that take?
That was a simplistic example, but do you see how Ti/Ne can get suppressed and Ti/Si get acceptable results? Other types may have similar responses instead of opposite ones, or even suppressed tertiary functions. Therefore not everyone will experience this, and other people may have a supportive person in their lives.