What's one thing that turned out way more complicated than you expected when building solo?

Been building something on my own for a while now and keep running into stuff I genuinely didn't see coming. Not the big obvious things like fundraising or hiring, more the small operational stuff. Legal paperwork, security compliance, the boring admin side of running a company.

Curious what caught other solo builders off guard. Not looking for "everything is hard" answers, more the specific thing you didn't expect to eat so much time.