Harry Potter didn’t actually save the Philosopher’s Stone. In fact, by trying to be the hero, he unknowingly did exactly what Voldemort couldn’t: he made the Stone accessible to him.
Dumbledore had constructed an elaborate security system around the Stone, with multiple obstacles designed to delay anyone attempting to steal it. A three-headed dog, Devil’s Snare, flying keys, a deadly chess match and a potion puzzle all stood between an intruder and the final chamber. Each obstacle required a different skill, and together they were meant to buy Dumbledore enough time to discover the intrusion and return.
But the real genius of the protection was the Mirror of Erised.
Dumbledore enchanted it so that only someone who wanted to find the Philosopher’s Stone without using it could retrieve it. Quirrell, acting on Voldemort’s behalf, was therefore completely helpless. He desperately wanted the Stone to restore Voldemort, meaning the mirror would never allow him to obtain it. He could only watch himself presenting the Stone to his master without ever being able to touch it.
Had Harry, Ron and Hermione simply stayed in their dormitory, Quirrell would have remained trapped in front of the mirror until Dumbledore returned.
Instead, Harry intervened.
Because his only intention was to prevent Quirrell from getting the Stone, the mirror recognised his intentions and placed the Stone directly into his pocket. Without realising it, Harry had removed the very object Quirrell couldn’t retrieve himself and brought it within his reach.
What followed was no longer a perfectly controlled security trap. It became a physical confrontation between an eleven-year-old boy and a professor possessed by Voldemort.
Harry survived because of the protection left behind by his mother’s sacrifice, not because his decision to intervene was particularly clever.
The irony is that Dumbledore’s security system was already doing its job. Harry’s attempt to save the day was what turned an impossible theft into a potentially fatal confrontation.
Did Harry Potter actually mess up Dumbledore's plan by trying to protect the philosopher's Stone, and what was the plan supposed to achieve?