After third year I got curious and started to research just what the Patronus charm is because there is so little understood about it other than you need happy memories and it'll be an animal that fights dementors and lethifolds, and after researching I managed to dig an extremely old tome that was barely legible cursive half the time and the other half it was bordering on actually being written in Greek. In this book, I managed to stumble upon the best piece of information I could have. The dementors aren't driven away by the positive emotional aspect of the Patronus, they're driven away because both the Patronus and the dementors are spirits. The charm isn't a charm at all, it's summoning magic. How nobody clued in on this, me included, mystifies me given the incantation literally means "I expect a guardian"