This is an unfortunate and pervasive problem with WWN.I am trying to understand the system for Renown and major projects, which turns out to be quite difficult because the actual rules are hidden within walls and walls of examples.
There are two ways PCs can go about acquiring enough Renown to complete a project. They can earn Renown by adventuring, but they can also take steps to decrease the difficulty. The “Decreasing the Difficulty” section describes several ways PCs can go about doing that. The reason for the distinction is that Renown gained towards decreasing the difficulty of a project does not affect the PCs’ own Renown.What's the difference between the difficulty and the renown cost for a project? In some paragraphs they seem to be the same thing, but in other places they are mentioned as two separate things the PCs have to deal with.
For example, while trying to establish a trade route, the PCs spend 50,000 sp buying off bandits and recalcitrant officials. That’s enough sp to purchase 17 Renown, which reduces the difficulty of the project accordingly. If the PCs had 10 Renown before they started bribing everyone, they’d still have 10 Renown afterward (plus whatever they earn normally per “Renown Rewards” on pages 254–255).