In philosophers stone - what was it that prevented Quirrel from attempting to get the stone before Harry had worked out how to get there and stop him?

I mean Harry thought Snape needed Quirrels 'bit of hocus pocus' to get through, but since it was Quirrel all along, surely the only thing in his way was getting past Fluffy? And it was weeks after the Dragons egg when Hagrid accidentally spilled the secret when Harry got down to the stone.

What was it that held Quirrel up?

I understand that he possibly didn't know all of the other teachers defences, but how on earth would he find them out?

Hogwarts MysteriesWhere stories live. Discover now