The manual gives me a clean answer, and then I open up a wall in an eighty-year-old building and nothing matches. The pipes go where they shouldn't, the layout makes no sense, and the textbook has no page for this. I'm standing there trying to figure out how to make the right thing fit the real thing.
More people experience this than they realize.
The clean textbook answer keeps colliding with the messy reality of an old building.
If this sounds familiar, the Library can help you find the bigger picture.