Again, being able to live a life of leisure exclusively out of your fortune's interests reaches far higher than "living a comfortable line". You can live very comfortably with a part-time job, or even a full-time job that's not too demanding.
The question says "without thinking about finances again". It is true the number could be lower, but there does need to be some buffer here. Otherwise you're one mistake/accident/recession/layoff away from "thinking about finances again".
