Gathering
In order to use the mastered skills of a craft, you will need materials. Some of them may be bought from the Monesy, however majority of the materials is so unique and valuable, that they are sold only very rarely.
Today, the best source of materials is own work and constant searching. Therefore, adventurers going to Tamrel must have knowledge of Herbalism, Mining, Archeology, Skinning and Disenchanting.