Ron's Joke Accidentally Exposed Voldemort Back in Chamber of Secrets, And No One Noticed
During their time studying in Hogwarts, the main characters were most definitely neither fond of Divination nor successful at it.
It was, in fact, one of their most hated subjects. They were not alone: most other students considered Divination classes a complete waste of time and called Professor Trelauney a fraud.
However, while the classes were terrible, divination in itself was not. Prophecies were crucial in Harry Potter, specifically the one about Harry and the Dark Lord (produced, ironically, by Trelauney).
There were also the centaurs who used completely different divination methods that allowed them to foresee grand events and processes. And then, there was Ron Weasley.
Ron was never Professor Trelauney's favorite student, and his Uranus joke didn't exactly improve his standing with her.
Luckily, Ron didn't need Trelauney's approval, since he could see into Voldemort's past just as well as she had seen into his future back in the day. After all, Ron exposed Dark Lord's past crime!
When Harry and Ron saw some Tom Riddle's award for special services to Hogwarts, Harry wondered what could that student have possibly done to deserve such an honor.
"Maybe he murdered Myrtle; that would've done everyone a favor," Ron, being the great master of past and future, replied to him.
He was correct, of course.
The student that received the award, Tom Riddle, was already on his path to becoming Lord Voldemort. Tom unleashed the basilisk and killed Myrtle with it, presenting Hogwarts with its most annoying ghost to date.
Ron exposed Voldemort without breaking a sweat — but you can't expect any less from Ronald Weasley, can you?
However, it was not what Tom Riddle received the award for: most likely, if someone realized that the eternal presence of Myrtle the ghost was his doing, he would've been stripped of the award instead.
Fortunately for Tom, this crime remained unsolved back in the day, and becoming the Darkest wizard terrorist of all time was not enough to remove his name from the Hall of Fame.
But we're telling you: if detective Ronald Weasley was on this murder case back then, Riddle would've been exposed in no time.