My friend,

The cards before you will take you on a journey into the minds of the Drylanders, a journey that for your safety you should take before you depart into the dry lands. These cards sum up the wisdom won by many daring spies, not all of whom could return to paint their own tales. But because of this wisdom, won by blood and cunning, you will travel into the dry lands armed with knowledge, and return alive to paint new cards into this deck. Each generation of spies goes into the dry lands more prepared than the last. And none has been as well armed as you.

Supplemental: Wisdom of Sorrow article.