You're simplifying what composes a "person" to a large degree. You can't default undo years of conditioning in the developmental years with one or two or a few positive influences later in life. It can happen, but it usually does not. That's just how chance works.
I mean, you're bringing up "parents and teachers." Read that case study I linked to. The parents had even worse upbringing than their children, and their parents than them and so on until you get to the ridiculously low start they had in this country (as compared to, say, hard working immigrants who worked hard to get here and would instill that, and their hope, to their children as a default). As stated in the linked thread - it's not rocket science to figure out how the people that are mostly descendants of slaves or descendants from people that were almost genocided and then shunted off into bad living conditions are doing the statistical worse of any ethnic group in the U.S.
Aboriginals in Australia have some similar aguments put forth against them. After being forcibly killed and subjected and treated as second class citizens, they're now living in poverty in statistically large numbers and prone to the violence and crime that goes along with poverty among any people, and you have a lot of Australians asking "why don't they just pick themselves up and educate themselves"
Do you understand how outside influences shape every single thing about a person? People are basically asking why a person with a ratio of 10 bad influences to every 1 good one can't have ignored all of those influences in their entire life for the few good ones, because someone with a 10-4 good to bad ratio on the other side took advantage of their good influences. Chances are, someone with more bad influences, from early in their life on, will have their minds shaped by those influences, and miss or not take advantage of the relatively few good ones.
That's just unfortunately how life works, which is why the goal is to increase good influences from the outside (telling parents who have been similarly or worse influenced, with less education and taught reasoning ability and little hope or perspective, to "do better" when the focus in their lives is day to day survival in already bad conditions aint going to work).
