Is business success due to luck or sustainable work ?

Definitely both!

I am gonna bring a third element to the table that is a good network. I've seen people getting into Y Combinator with nothing valuable in their hands just because they had a good network :-)

There's certainly a lot of work involved, but as they say you have to make that luck happen!

I usually don't really believe many people are much more lucky than others in the vastness of the business world. I think recognising and taking advantage of luck is what really counts. People have luck, connections, and opportunities right under their nose that they can't see the potential in. It goes without saying though that most (including myself) believe sustainable work is crucial!

I think both, but sustainable work is a significant contributor to success.