We all make mistakes – and that applies whether you’re the wisest wizard in the world, the Boy Who Lived or the Dark Lord. But which errors were the most devastating for the wizarding world?

Cornelius sending Hagrid to Azkaban

Cornelius Fudge, Minister for Magic, was definitely a career politician, a self-serving tyrant without principles who rarely considered anything but his own importance. When he turned up at Hagrid’s hut in Harry Potter and the Chamber of Secrets to take Hagrid to Azkaban, he displayed the sort of petty bureaucracy and self-preservation that would become his hallmark: ‘I’m under a lot of pressure. Got to be seen to be doing something,’ he said, blaming Hagrid for opening the Chamber and releasing the Basilisk.

What he was actually doing, though, was sending an innocent man/giant to the most horrifying place we’ve ever heard of – an offshore prison staffed by Dementors where inmates were depressed to death. It’s a testament to Hagrid’s strength of character that he recovered after release, only once telling Harry, Ron and Hermione about his experience: ‘I used ter hope I'd jus' die in me sleep.’ All on your conscience, Fudge.

Voldemort thinking Snape was Master of the Elder Wand

The Elder Wand had a long and bloody history stretching back centuries, and its owners, from Antioch Peverell through Emeric the Evil and Gellert Grindelwald, sought to become masters of death by winning its allegiance. Voldemort knew this and needed it for himself, so when Severus Snape killed Dumbledore in Harry Potter and the Half-Blood Prince, he assumed Snape was the new holder. He was wrong: Draco Malfoy, having disarmed Dumbledore shortly before, was now its master.

So when the Dark Lord ordered Nagini to finish off Snape so he could claim the wand, he was no closer to his dream of immortality. And in the end, this mistake spelt the end of Voldemort too, when his Killing Curse backfired from the Elder Wand at the Battle of Hogwarts. The take-home: do your research before you act.

Barty Crouch Sr breaking his son out of Azkaban

Barty Crouch Jr was a nasty piece of work, taking the Dark Mark at an early age and showing fanatical support for Lord Voldemort. His father Barty Sr, as a member of the Council of Magical Law, sent him to Azkaban for torturing the Aurors Frank and Alice Longbottom, but even then a mother’s love shone through: she persuaded her husband to allow her to switch places with her son in prison using Polyjuice Potion. Big mistake. Although Barty Sr kept tabs on Jr for a while with an Imperius curse and Invisibility Cloak, he broke free at the Quidditch World Cup in Goblet of Fire and began causing havoc on behalf of Voldemort once again.

And what havoc – he assumed the appearance of Alastor Moody, sent an underage Harry into the Triwizard Tournament and caused the death of Cedric Diggory. Barty Sr, we know he was your own son, but it really would have been better to leave him where he was.

Harry’s misplaced bravery led to Sirius’s death

Aware of how susceptible Harry’s mind was to the intrusions of Lord Voldemort, Dumbledore pressed Professor Snape to teach him Occlumency to defend himself in Order of the Phoenix, but to no avail. Harry was too curious about what was in that orb in the Department of Mysteries, so he travelled there in his dreams and was tricked by Voldemort. Not for the first time, we admired his bravery when he stepped up to save his beloved godfather; not for the first time, Harry proved his fallibility, but as ever he acted with honour.

That may have been scant consolation for him, however, as he struggled with the deadly consequences of his actions – he’d felt the pain of losing someone close to him, again, this time more acutely than ever before.

Dumbledore wore Marvolo Gaunt’s ring

For anyone who knows wizarding history, the Resurrection Stone is clearly not to be messed with. For one – legend has it – it was made by Death himself. It drove its first owner, Cadmus Peverell, to suicide. It was set into a gold ring, which Tom Riddle Jr stole after murdering half his own family. Although he knew its terrible power, Dumbledore couldn’t help putting it on in the vain hope of seeing his family again in Deathly Hallows, proving that even someone so wise and worldly is not immune to the temptations and feelings that face us all in life. ‘I… was a fool,’ he said. No, Dumbledore, you were only human.

Sirius Black made Peter Pettigrew a Secret-Keeper

When Lily and James Potter hid out in Godric’s Hollow during the First Wizarding War under a Fidelius Charm, they needed someone to hold the secret in their soul. Sirius Black, a great choice, thought Voldemort had him figured out, so he passed the responsibility on to Peter Pettigrew. Not a great choice.

He was already traitorously spying on the Order of the Phoenix for Voldemort, and immediately informed his master of the whereabouts of the Potters. They were slaughtered by the Dark Lord, leaving the infant Harry an orphan. Without this betrayal there would have been no living with the Dursleys, no deaths of dozens of blameless wizards and Muggles, no more war. Peter, it didn’t have to be this way.