Page "Amber Diceless Roleplaying Game" Paragraph 26

While a character with Pattern, Logrus or Conjuration can acquire virtually any object, players can choose to spend character points to obtain objects with particular virtues-unbreakability, or a mind of their own.

Since they have paid points for the items, they are a part of the character's legend, and cannot lightly be destroyed.

Similarly, a character can find any possible universe, but they can spend character points to know of or inhabit shadows which are ( in some sense ) " real " and therefore useful.

The expansion, Shadow Knight, adds Constructs-artifacts with connections to shadows.