It's not an either/or: almost every successful company requires both hard work and luck. In very rare cases one or the other might be sufficient, but in the vast majority of cases both are necessary. The amount of luck required can be reduced by hard work, but it can't be taken to zero.
In the usual case, picking a product that turns out to have high demand is the biggest area where luck matters.
There are two kinds of high-demand products: the things that everyone wants but no one knows how to do, and things that no one knows they want but everyone knows how to do.
Fractal image compression is a good example of the former.
Almost everything else is a good example of the latter: smart phones, Facebook, Twitter.
There are some things that are both: the Model T ("If I'd asked my customers what I wanted they would have said a faster horse") and so on.
If you choose one of the former, the odds are you'll fail because if no one else can do it, you probably won't either.
If you choose one of the latter, the odds are you'll fail because if no one knows they want it, it's probably a stupid idea--which is often a smart idea whose time has not yet come.
This is not to say you shouldn't go for it! "The odds are you'll fail" is a simple statement of fact with regard to starting a business, but only for certain values of "fail". You'll learn a huge amount, grow in ways you never knew were possible, and have the adventure of a lifetime. Just be really, really careful about not getting wedged financially, and especially make sure you don't let friends or family members over-invest.