Sirius Black is one of the supporting characters from Harry Potter who had a huge impact on Harry as well as on fans. He’s still a fan-favorite character even though he really only appears in three of the books. He’s a rather complex character that’s overall good but has a lot of flaws. These nuances combined with his rather tragic backstory make him compelling.
While Sirius might not be a main character, he does make a lot of choices that impact the narrative of the series. While some of these choices are good, he also makes some pretty obvious mistakes that impact other people. This doesn't mean all of the effects were bad, but they did change the course of the story.
Bullying Snape too much
The relationship between Snape and the Marauders was bad all around, but it’s too simplistic to paint Snape as the victim and the Marauders as the bullies. Snape was dabbling in dark magic, so it’s no surprise others didn’t like him.
However, the way that Sirius and James took punishing Snape into their own hands often went too far and was not always motivated by pure motives.
Letting his emotions get the better of him
Sirius is an interesting character precisely because he’s not completely logical or rational. He can be over emotional and is quick to anger and make rash choices. However, this can lead to him being difficult to be around.
He made things difficult for the other members of the Order and for Harry When he was angry about being stuck in Grimmauld Place.
Running around the grounds with the Marauders
While the Marauders did have an overall immature disregard for rules, probably the worst thing they did as students was to have Lupin run around the grounds while as a werewolf.
While Sirius and James might have thought they had things under control, it was reckless and dangerous. Luckily, nothing too bad happened, but the fact they didn’t reveal their animagus abilities did impact the story in Prisoner of Azkaban.
Not killing Pettigrew in Prisoner of Azkaban
This is one choice Sirius makes that can be looked at from many different angles. In some ways, it seems like a major mistake because if Pettigrew had died Voldemort might not have come back to power.
On the other hand, Voldemort might have come back to power anyway, and Pettigrew ended up saving Harry’s life inadvertently. Either way, this decision did have far-reaching impacts.
Being violent when breaking into Hogwarts
When Sirius is trying to find and kill Peter Pettigrew, he doesn’t go about things in the best way. He is clearly still dealing with the cruel and unusual effects of Azkaban, and his anger and suffering drive him to break in.
He fights Ron and the other students, and he even breaks Ron’s leg in an accident when dragging him into the Whomping Willow.
Encouraging Harry to be reckless
Sirius clearly cares a lot about Harry and wants to be a godfather to him. It’s clear he feels guilty that he wasn’t able to be there for him for so many years, and there are many instances of him being a good godfather.
However, he also makes some bad choices for Harry. When he gets moody with Harry for not breaking rules around Umbridge and tries to guilt-trip him, he’s being immature and selfish.
Going to King’s Cross in his Animagus form
This decision was a bad one and basically everyone around Sirius told him not to do it. However, Sirius can be arrogant and doesn’t like to be told what to do. So, when he chose to accompany Harry to King’s Cross, he might have thought it was harmless.
But, this decision did tip off the Malfoys and others to Sirius’s whereabouts. Luckily, he was able to stay hidden at Grimmauld Place, but it did let others know that he was alive and around.
Going to the Ministry to save Harry
Not all mistakes are made out of bad intent, and there are even some mistakes that probably had to be made. When Sirius goes to the Ministry to save Harry and the others, it makes sense that he would do so.
It’s hard to imagine him not going to help. However, this decision is a mixtape in the sense that it leads to his death. However, it was a risk that he and all of the Order members took.
Nearly getting Snape killed
Once again, Snape isn’t nearly as innocent as some fans like to make him out to be, and he was a pretty deplorable person in many ways. However, it wasn’t Sirius’ job, especially as they were both teenagers, to try to get Snape killed.
He wasn’t judge, jury, and executioner, and he also put Lupin’s safety at risk. If Lupin had killed Snape, it would have been horrible all around.
Making Pettigrew the Secret Keeper
This is another mistake that was made out of the best intentions. Sirius did the best he could with the information he had, and he was trying to protect the Potters.
The blame for what happened rests with Pettigrew, not with Sirius. However, it’s still a tragic choice that had major consequences, and it’s definitely a choice that Sirius regret making.