#7: Tom Riddle basically defeats himself
Next up: at the end of The Chamber of Secrets, Harry enters said chamber of secrets with, give or take, zero idea of what to expect or how to deal with it. Luckily, when he's face-to-face with Tom Riddle, still not really sure what's going on, Tom decides to go full James Bond villain and delay killing Harry in order to explain everything in great detail. Who he is. What he's done. What he intends to do. It's...pretty comprehensive. This has the effect of not only giving Harry the information he needs to defeat the ghost of Tom Riddle and save the day, but it also provides the opportunity for Harry to demonstrate loyalty to Dumbledore, which directly leads to the phoenix swooping in to save the day.