Those are words no parent wants to hear. There is a type of child abuse though called covert child abuse. We have to be careful because many times this is associated with "Munchhausen by proxy". However, there is another form. This other form has the form that the child is ignored, totally. Lets take an example. Suppose Johnny was in first grade and did not do his first home work assignment. What does that really mean. Nothing. It means Johnny did not do his first home work assignment. No more; no less. Now add in the following. No parent even knew there was home work, no parent asked to look at it, check to see if it was done, or anything. How does Johnny feel? Good question. I do not know. He's six. He feels but does not know how to analyze feelings or even what to do with them. It's covert; no overt like "I feel hungry." He does not know enough to go to his parents and say "parent me." Now Johnny goes to school, does not have his homework so he lies, my dog ate it or whatever. The lying worked, or so he thinks - it does not matter, it now becomes a tool for his covert life. "If I'm ignored, I can lie and no-one will know, I can do things and no-one will pay attention and know, I can become whoever I want (falsely)" plus a host of other behaviors.
Now fast forward a few years to a project Johnny is working on. It's been a few years, Johnny developed an interest on his own in third grade and learned what he could. But of course no-one else knew, why bother even telling them at this point. As a matter of fact, the thought does not even cross his mind. He tells other children but they do not understand. That's okay though, they are not his parents. He is disappointed but associates "with a child's mind" that no-one, even his peers care. No-one asks, cares or inquires in anyway about it. Johnny by this time cares but does not care. He has learned to manufacture a bubble around him so that even if someone cared, he would not trust it.
However, Johnny's feelings are not totally dead, at the school wide showing of the projects, his parents go through the motions of attending, but they are just the required motions and the minute they can leave they do. Maybe Johnny gets asked a question about his project which he answers incorrectly. Although he knew a lot and had interest, this is met not with parental interest in explaining the mistake, and patience; but simply criticism. Now Johnny feels stupid too.
Of course these are two things which Johnny remembers. There are probably hundreds; but the mind can't handle that as a child or adult and rolls it in to a form it can remember best; a couple of instances. But the baggage: slews of learned or figured or behaviors-real or not; correct or not.
So by the age of 10 Johnny feels others do not really care, he feels dumb and he has learned to trust the covert world of lying and distrust others. Through watching his peers, he starts to understand that this is not what other's lives are like and that it must be him. He sees the overtly abused child and feels bad about himself for having his feelings; he is not beaten. He feels shame and self loathing. He must be wrong and bad; why else would no-one care?
It does not really matter why Johnny's parent's are so ignoring of Johnny. Why they only care about themselves. What matters is what Johnny is learning. Maybe they are alcoholic, recovering alcoholics, maybe they are over compensating for their childhood; whatever. But they do not have time for Johnny; not real time. They might fake it. By now Johnny can see right through, does not trust it, and it simply reinforces his feelings; which are no longer feelings; they are beliefs that really he is a piece of sh_t. It's okay though (not really). He has a covert life and can pretend all is okay. He can lie and make others believe what he wants (actually just those who don't really pay attention.)
At some point in a child's life, 14 or so, when they start to become their own person they begin to understand that something is not right. Two paths are typically taken. One path leads to the child who acts out by getting in trouble to force attention and caring; positive or negative. The other simply recedes in to the shadows and has learned how to make everything appear okay.
What happens to that child when they grow up? I do not have an answer other than to say that grown up Johnny is still the 6 year old who did not do his first home work assignment and no-one knew, cared or paid any attention.
Johnny, being the "okay" teen may even be put in charge of the ignored other sibling who took a different path. Johnny learns fear and power. More tools. If he succeeds, it is because he faked it (at least that is what he believes deep down inside.) He is praised but he knows it he faked it and it reinforces his feelings (which have now become behaviors) of his own "covertness". If he fails, that's even worse. Now he knows he cannot fail. He fears failure. He fears the loss of control that he has learned to embrace.
What happened before 6? Between 6 and 10; and thereafter. Many things I'm sure. I do not have answers.
This is all just food for thought; fraught with gaps and questions but also of the beginning of important understanding.
None of us is perfect parents (I don't think) but we need to parent as best we can. At least let our children know that we know about them, what they are doing and give them the attention that steers them towards what we feel is correct behavior. They need to know we know.
Johnny did not have that and probably still does not. Even if he does, he has learned to not trust it.