Rare and special knowledge is not readily available to all members of some professions, even if they know their trade well. For instance, to have even a small chance of success, you must know how to mix certain formulas or work rare materials to craft true masterworks. These trade secrets are what make it possible to create the extraordinary, and such knowledge is usually very closely guarded. Trade secrets pass directly from masters to students or other individuals as special signs of respect and honor.
Core Rule page 187