One of the main markers of a startup is there tends to be One Big Challenge to get the company to The Next Level (generally talked about as a funding round, but that's just a convenience). Initially you're finding product / market fit, then you're figuring out a scalable go-to-market, then you're scaling the product, then you're launching a new product, etc.
It's weird to go through one of these transitions, because you'll need to change your focus pretty drastically. Sometimes you'll feel sidelined, because your department isn't the one primarily on the hook. If you're figuring out how to build a sales team, engineering gets chill and potentially complacent. The most successful startups have leaders that paint a clear picture that gets all departments working autonomously towards the same goal.
This is different than a smallco, because without a war chest of cash, your options are more limited. Because cash flow dictates the cadence of the business, and that's never going to change. This can feel more stable, but does mean you'll have to occasionally make hard choices that delay a valuable project or work on something outside your speciality.