Depends how you define success. Since this is the Jobs forum I assume it is career success. I think there is a luck factor in being born into a wealthy family and getting a good education. It still requires hard work though, unless you're just given your father's company, or hooked up with a great job by someone you know.
It's possible for luck to be the main factor. If you have someone who's an okay employee (does the job, but isn't a particularly hard worker, and isn't particularly smart), they can do well based on luck (their mistakes sometimes go unnoticed, or occasionally actually work out; they happen to be in the right place at the right time to prevent something really bad from happening; etc).
Luck has a lot to do with landing your job but once you're in your position you need to work hard and smart in order to become successful. However, I will say that the hardest part about working IMO is getting the interview and job offer. Once you've been hired they can usually train you to do whatever it is you need to do.
Luck alone may not make the person successful in the career. There's always work involved. However it's not to say that success is only due to hard work. I think luck - being at the right place, at the right time, with the right opportunities/contacts, play a significant role too.
Combination of both luck and hard work in most cases, but can be almost purely hard work, or almost purely luck. I'd say if you get lucky and land a very successful career, you deserve it if you continue to work hard to keep it.
If a=1, b=2, and so forth until z=26, then. . . . . . .
H-A-R-D-W-O-R-K would add up to 98% (8+1+18+4+23+15+18+11)=98
K-N-O-W-L-E-D-G-E is 96% (11+14+15+23+12+5+4+7+5)=96
A-T-T-I-T-U-D-E is 100% (1+20+20+9+20+21+4+5)=100
B-U-L-L-S-H-I-T is 103% (2+21+12+12+19+8+9+20)=103
And, look how far feet kissing will take you. A-S-S-K-I-S-S-I-N-G=128%
numerically represented 1+19+19+12+9+19+19+9+14+7=128
So, one can conclude with mathematical certainty, that while Hard work and Knowledge will get you close, and Attitude will get you there, it's the Bullshit and Ass kissing that will put you over the top.