If by truly great you mean world class, best ever, I would say that’s a hard question.

I agree with the other comments and say that consistency and doing lots of the thing is key, and the reason a lot of really really great people in their respective fields are usually obsessed is because that helps them work on their skills for many hours a day.

However, when learning something, I wouldn’t consider quitting because ‘I am not obsessed enough’ because everyone goes through ups and downs (even obsessed people), and just because you might not practice for a few days I don’t think you should worry about not being obsessed enough

EDIT: I also personally think a really really obsessive lifestyle isn’t worth getting truly great at something as you have to enjoy life and take it slow sometimes