You don't even have to work that much harder. What matters is the output. And those of us coming from overpopulated underdeveloped countries have been forged in an environment where you need to have a hyperactive attitude to outcompete your peers. I don't work any harder than American students at my grad school, and my professor doesn't want me working after hours either. Many of the faculty I'm familiar with basically say that they've started preferring East Asian and South Asian students because they can be more productive and more interesting than American students at the same time. All the Asian grad students here seem to be top of the class, high up in citations, pop culture nerds, classical musicians, sports heads, fitness enthusiasts, technical gurus- all at the same time.