Some people are really good at that initial torque boost on projects and can sustain it longer than others, but if work doesn't get easier it's because you're doing something wrong.
From a market-fit perspective, I think startups that drive around in first gear never get very far either. Things are only hard because we're being stupid. Nobody ever looks at a person driving a ferrari and thinks, "wow, they must have washed a lot of dishes to afford that car," and yet we still think "if I just wash these dishes hard enough I'll drive a ferrari one day."
I'm guilty of this as much as anyone, but burnout is my body intervening to tell me I'm being stupid.