If Harry hadn't lept up to protect Sirius from Dolohov, and Sirius got cursed like Hermonie, maybe he wouldn't have had to fight Bellatrix and survived . . .😥
But Harry did. it's not Harry's fault for doing that though. He needed protecting then, he wasn't going to know what was going to happen in the future.
Harry could be blamed for rushing to the Department of Mysteries without properly confirming that Sirius was there. He should have spoken to Snape instead of breaking into Umbridge’s office. Snape would have been rude and sarcastic, but he would have been able to quickly confirm that Sirius was fine.
