"The teenage Sirius was, in Remus’ words in OotP, ‘the height of cool.’ He’s remembered by his former Head of House and other teachers as academically brilliant, he was wealthy and apparently something of a school heart throb. So far, so idyllic and what possible problems could a boy like that have?
Well, the Noble and Most Ancient House of Black for starters.
It’s all too easy—and common, in my experience of fandom—to write off Sirius’ disconnection from his family, as if he were merely a rebellious child who traded the family he was born into for the one he created with no apparent difficulty or consequence. In truth, it was unlikely to be so easy and we can see the evidence of the trauma Sirius experienced at the hands of his family in the adult he grew into. The Black household, it is safe to say, is not a particularly loving one; indeed, even the house itself gives Harry the creeps with its strange bottles of blood, pots of poisonous powder and violent snuff boxes. Sirius’ mother’s portrait shrieks insults and racial slurs at all and sundry, with the same abuse being echoed by the House Elf, Kreacher. This is a family with an exceptionally high opinion of itself, ‘convinced that being a Black made you practically royal,’ with long standing tendencies towards a love of violence (attempting to legalise Muggle-hunting) and the macabre (mounting the heads of dead House Elves on plaques). It’s rather hard to imagine that Orion Black might have given the infant Sirius and Regulus piggy-back rides around the library or hugged or tickled them; harder still to envisage Walburga Black cuddling her sons or rocking them back to sleep when they woke from nightmares induced by the various Dark Arts paraphernalia around the house.
Most telling in Walburga’s attitude towards her eldest son is her decision to blast him of the family tapestry. In itself, this may seem fairly trivial; it’s only a tapestry, after all, and Sirius had already left, so what did he care? It matters because it gives an insight into her feelings about Sirius. The tapestry is a record of who belongs to the family—in removing Sirius, she is pretending that he doesn’t even exist. Plenty of parents despair of their children, many are even estranged from them, but few ever wish to deny their own child’s existence. Denial of a child’s existence is not the act of a loving parent.
Did the Blacks ever really love Sirius (or Regulus, for that matter)? After a fashion, perhaps they did. The heir apparent of the Noble and Most Ancient House of Black occupied an important position in the family as the future head of the family--the importance of this role is emphasised in his parents’ choice of given name, as we see from the Black family tapestry that Sirius was name frequently given to the heir. Prior to his rejection of the family’s pure blood mania and snobbery, young Sirius may well have been highly valued. However, being prized as an heir is very different to being loved as an individual.
Children need to be loved, and they need to be loved unconditionally. The Blacks may have loved Sirius when he was very young, but they only loved him as long as he acted and thought in a way they approved of. A child who realises that their parents’ love is conditional will be emotionally damaged, either because they don’t meet their parents’ ‘conditions’ for love, and therefore have that love withdrawn (like Sirius), or because they must constantly struggle to ensure that they do meet the conditions so that their parents will continue to love them (perhaps, like Regulus—I do think that Regulus was damaged by his parents as well.)
I picture Sirius as being rather spoiled when he was young - a little like Draco or Dudley, a pampered prince. The Blacks thought they were practically royalty, and would have encouraged their son and heir to think of himself very highly - that he, as a Black, was somehow ‘better’ than other people. This position may seem an enviable one and had Sirius accepted his family’s ideology he may well have been quite happy to receive the attentions and favour due to a Black heir without questioning whether or not his parents were actually bother about him as a person at all. Trouble is, Sirius was way too smart not to see through all that bullshit. We know that Sirius was exceptionally bright and, more to the point, he was capable of using his intelligence without direction—he was an independent thinker. Most children are good at questioning things, bright kids even more so, and I can imagine the young Sirius coming up with a hundred and one questions that would have shot holes in his family’s racist ideas. ‘Why can’t I play with the Muggle children in the street, they look all right to me?’ ‘What are all those burn marks on the family tree for?’ ‘What’s wrong with marrying a Muggle?’ ‘Why do the House Elves have to wear tea towels?’ ‘Why is it better to be a pure blood?’ That’s a lot of questions that the elder Blacks would have no logical answer for, because there is no logical basis for that sort of elitism and prejudice. Ultimately the only answer they can give is that this is what’s expected of a Black; it’s what makes us special.
As he grew older, Sirius came to realise that the things his parents most valued in him were essentially worthless. His parents may have believed that being a Black made you special and important, but Sirius saw his position in the family for what it was—a mere accident of birth. He didn’t pass exams or win fights to become the heir, he wasn’t selected by an all-England committee as the most deserving young wizard of his generation to earn his destiny as scion of a wealthy and influencial dynasty; he was just born that way. What conclusion could the young Sirius draw from realising that the most important thing about him didn’t have any real value? That he doesn’t really matter.
To say that Sirius suffers from low self esteem may at first glance seem like a rather extraordinary suggestion, given that he is, with some justification, often seen as an arrogant little blighter. However, Sirius’ arrogance is limited to his estimation of his capabilities and this ‘arrogance’ is often justified. (Is there any real doubt that he did get an ‘O’ for his Defence Against the Dark Arts OWL?) Despite having a high regard for his abilities, Sirius appears to attach little value to himself as a person. Sirius is often described as reckless, yet for the most part he is reckless about his own welfare. He repeatedly puts himself in dangerous positions and never gives any real indication of caring much about what happens to him. We never hear Sirius complain about how awful it is to life in a cave in Scotland or spend twelve years in Azkaban, nor does he ever express any concern about his own safety or welfare. Of course, Sirius isn’t some sort of long suffering saint and he does sometimes display bitterness about the more grievous injustices he has suffered, but he never acts on the basis of doing what is best for him.”
"Sirius’ extreme and forceful personality is partly a result of the break from his family, but it was also part of the cause of it. At the age of eleven Sirius became the first Black not to be Sorted into Slytherin in centuries and he was later able to deliberately and consciously reject his family’s pure blood supremacist politics and affiliation with the Dark Arts. To be able to do this required a powerful personality and certain amount of innate anger; Sirius’ sense of absolute outrage at his parents’ bigotry was such that he literally couldn’t stand to be a part of the family. Note that when Sirius talks about his little brother’s decision to accept their parents’ racism and join the Death Eaters he doesn’t describe Regulus as evil or as being a committed pure blood supremacist himself, he says he was ‘soft’ and an ‘idiot.’ This suggests that, in Sirius’ opinion at least, Regulus lacked the qualities that Sirius had to possess in order to get away from his family—the strength to stand up to his parents and the intelligence to see the wrongfulness of their ideas.”