Personality doesn't necessarily have anything to do with either knowledge or character. Those are things that need to be cultivated. "Roots" are more than bloodline. They are the environment in which one grows up, what he learns to value, what he learns about love. How can a child who has never seen a good relationship know how to HAVE a good relationship or be a good mate...if, indeed, that child ever learns that a mate is anything more than a sperm donor or receptacle? How can a child who has never been parented know how to parent his/her own children? A child learns what a man is based on his/her own relationships with men, particularly his/her father. A child learns what a woman is by his/her relationship with women, particularly his/her mother. If these relationships are warped and twisted and ungrounded, it stands to reason that the child's view of them will be also.
A child learns what he lives, by default, and that learning forms the foundation of everything that comes after. If the foundation is false or unstable, how can that which is built on it be sound? A house built on sand might stand for awhile and a beautiful house can be built on a rotting foundation, but the foundation will ultimately collapse because it is unstable.
That's not to say that a child cannot rise above his/her circumstances and some of the desire to do so indeed is born of the innate personality, but it requires a lot of self-motivation that many of them just don't possess.
Believe it, it can be done.
Possibly as you say not often though.