It occurred to me that Professor Trelawney is the root of all evil in the Harry Potter series!
She made the prophecy which made Voldemort go after Harry’s parents.
If she hadn’t applied for the Divination job, Dumbledore, and therefore snooping Snape, wouldn’t have heard her prophecy.
Snape wouldn’t have told Voldemort about the prophecy and caused him to decide it meant Harry Potter.
Voldemort wouldn’t have killed Lily and James, and tried to kill Harry.
Voldemort wouldn’t have inadvertently turned Snape against him because he killed Lily.
Sirius would never have died in the Ministry because Harry would never have heard about it through Voldemort’s obsession with hearing it all, and wouldn’t have been tricked into going there to retrieve it.
Lily wouldn’t have died trying to save Harry, and given him the protective spell created by her sacrifice.
Harry would never have been made an orphan and forced to live with the Dursleys.
If Trelawney hadn’t made the prophecy about the one who could defeat Voldemort, Dumbledore would never have made her a professor, and then Harry wouldn’t have heard her make the second prophecy about Wormtail returning to his master.
If Harry hadn’t heard the second prophecy, he might not have discovered the truth about Sirius and Wormtail switching places as Secret Keeper for the Potters.
….and on and on it goes!