Uncertainty in Essay Writing: How do I know I will find a good argument?
Simple: You start exploring several ideas, gathering references, learning how the attempted solutions work, searching for possible extensions/alternative approaches.

As Edison said: "Genius is 1% inspiration and 99% perspiration". You'd have to put in the "perspiration" part to be able to see the "inspiration" spark. Or, as Pasteur stated it, "Chance favours the prepared mind".