True. The work itself has its own issues but hammering the requirements is the most difficult because it’s the most human.
People DON’T know everything they want when they start. So, it’s an iterative process.
The mistake a lot of folks make is expecting initial requirements to remain in place throughout the life of a project.
They don’t. They never do.
So you need to do things in iterations… or you end up playing the game of “But this wasn’t in the original requirements!” which, actually does buy necessary time.