At the end of The Sorcerer's Stone, Goblet of Fire, and Order of the Phoenix.
In The Sorcerer's Stone, even if Harry never went down to the place where the mirror was in the end, Voldemort and Quirrel wouldnt have been able to get the stone anyway because Dumbledore says only someone who didnt want to use the stone could get it from the mirror. If anything Harry could've only helped them get the stone.
In The Goblet of Fire, if Harry knew he didnt submit himself into the Goblet, then wouldnt he be more suspicious and wouldnt he withdrawl from the competition because someone obviously wanted him dead and in the end if he took the goblet by himself, Cedric wouldnt have died.
In Order of the Phoenix, if Harry didn't go to the Mystery place then the death eaters wouldnt have been able to get the prophecy anyway and Sirius wouldnt have died. If he was more serious about the Occlumency then none of it would have happened. The only good thing that happened was that the people knew voldemort was alive. I am a fan and friend of JK Rowling but she probably shouldve thought more about the plots before she wrote the books and had us act in the movies.