Dear Drabsv,
Psychologists might be able to answer this question better than I. However, with my experiences rearing two daughters and helping with four grandchildren (one of whom has recently made me a great-grandmother) and friends of theirs I've come to know, I'll be happy to give you my thoughts on the matter.
If a child feels the need to "assert" his/her position in the family, I would guess that there is a lack of communication between parent(s) and child. If this assertion first appears in the form of rebellion, I would susect that the child has deep-seated feelings of being "unheard" within the family, and lashing out is the only way such a child may respond. A child needs to feel that he/she is an important member of the family, whose opinions are at least heard and respected if not followed. Family discussions on all matters of importance should include all family members. Sure, the parents can discuss and come to conclusions in private, but their reasons for decisions should be openly discussed with family members, not strictly enforced with no form of dissent allowed to rear its ugly head. I believe that children who are given a voice in the family, who feel that their views are important -- even though not always given preference over others' -- at least know that they are not living in a vacuum where their individuality is of no concern.
As far as breaking away from parental protection and interference is concerned, I feel that if a child gains the trust of the parents from an early age, then "breaking" away may not even be a problem. This is trust that comes of a child always being honest, doing chores as expected, coming home from school on time, not "back-talking," and, generally, growing up learning that certain things are expected of a child, and if those things are not fulfilled without very good reason (no excuses), there are and always will be reasonable consequences. This is a continual process -- from not touching the crystal or leaving the yard to coming home from a date on time to not drinking while driving, etc.
If a child is always told "yes" to his/her every request (or demand, it seems, these days), that child will come to overemphasize his/her own importance and believe that the world should always conform to whatever the child wants, and if it doesn't, temper tantrums and worse will be the outcome. If a child is always told "no" to every request, he will come to feel unimportant, a pawn utilized only in the performance of duties for the parents' selfish aims. Both extremes should be avoided at all costs. A realistic view of the world is usually what is missing in both cases, and all too often, the lessons of the world eventually come at great expense to both child and parent. Unless the child is psychologically or mentally impaired, which is rare in the majority of cases, the parent(s) are ultimately to blame for not taking the time to instill in the child a sense of self, as well as the importance of learning right from wrong (actions vs. consequences, not restricted to but adding to religious upbringing), then the parent(s) and child will eventually come to realize the consequences, too often, all too late. The proper upbringing of a child is a parent's responsibility, not the child's, and great patience and understanding are required in all instances.
Once a child becomes a teenager, with all the influences inherent in today's society, much is already ingrained in his/her brain, and even more patience and understanding may be necessary to help the child attain maturity in the true sense. However, if a parent loves the child, this will be a sacrifice most welcome and well worth the additional effort required now that circumstances insist on change of one sort or another.