The details about the day-to-day operations disappear quickly as you move up the hierarchy.

My boss recently had a meeting with a large customer of us, we deliver a product used heavily by one of their departments. Here's roughly how that went down:

My boss: "Well, what about when you do orders of type X?"

Manager: "Oh we don't do those"

My boss: "Really?"

My boss brings up the order list and filters on type X, finds at least one entered each day by user ABC

Manager: "Oh... so that's what she does"

So that information was lost in just one level.

This is why we try our best to get the actual users involved when discussing requirements with a customer. I don't think I've ever experienced a project where at least one of the users haven't brought up some edge case the manager wasn't aware of or had completely forgotten.

On the flip side, the projects where the users are left out of it until it goes live never goes well. We'll get it fixed eventually, but there's always pain for far longer than necessary.