"Okay, imagine this. Your Growlithe is facing a Petilil and you click Ember for an easy 2HKO. Petilil uses Leech Seed and calls for help. Eight turns and a continuous chain of newly summoned Petilil later, Growlithe has been defeated by a Pokémon that it always 2HKOs and that can barely inflict 2 HP of damage on it. Does this sound in any way fair to you?"
Yes, because you were too stubborn to run after Petilil #3.