It isn't insanely hard IMO... getting there is the hardest part IMO.
Before I get blasted for making what could be perceived as a blanket statement, let say that personally I usually walk around between 8-10%... and I don't do cardio. I'd say I was a fatboy growing up. So, IMO, it's very doable.
(Right now i'm not at 10%... but that's a different discussion though)
How well do you deal with stress?
And how are your time-management skills?