Why did labor suck for you?

As a FTM, I know that labor is either horrible or magical and most likely a little bit of both. But since I don't really know what to expect, I'm wondering where, specifically, the horrible part comes from. Aside from the obvious (being incredibly painful), what makes labor suck? I'm big on preparing myself for the worst. And hopefully making plans to mitigate extra suckiness, if possible.