If someone is of average or higher natural ability, yes, hard work and perseverance will be the biggest determinant of outcome. But someone who's genuinely pretty dumb, wholly socially incompetent, or exceptionally disabled or ill will have massive difficulties being successful regardless of their perseverance.

Which isn't to say that hard work is useless to the people on the lower end of the spectrum: far from it, a stupid hard-worker not only can find themselves with a decent enough job but will usually be able to keep it. It's just they lack the ability to set themselves up for good opportunities like that and to limit downside risk from one-off events. Luck of the draw will end up dominating outcomes.

(Obviously, most people who comment on internet forums, particularly a specialized forum like HN, are not only likely to be average or above but also to have extremely limited contact with people significantly below the mean, so if you're reading this, your life outcomes probably are determined by your own work ethic. On that note, cheers to a productive Sunday!)