Dan had a really difficult childhood for sure, though there are conflicting accounts of how badly his parents neglected/abused him, if at all. It may be that they just couldn't deal with his tard rage, not everyone is cut out for that. But by his early teens his grandmother had custody and he was enrolled in a special school, and he even made the news as a sort of feel-good story. It looked like he was going to have if not a normal life, then at least one where he was safe and as happy as he could be. Then his grandmother died, he graduated tard school, and that's when he went of the rails.
It's a big problem in my country (UK) and evidently in America too - the child care system just chucks people out on the streets when they hit 18, when people like Dan aren't mentally adults and never will be. It's not like he was any more capable of looking after himself at 18 than he was at 17. He went from being looked after to having the rug pulled out from under him and being judged by adult standards, whereas Dan even now seems to have the intellect and understanding of the world of a 5 or 6 year old child. Dan was let down by his family and the system, then fell into the clutches of Discord psychopaths who make him suffer (and put the people around him in real danger) for their entertainment.