Material difficulties are increased by 5, and you can only gather materials equal or lesser than your skill level. Most materials spawns allows up to 3 chances to extract material from it, some special materials might only allow one chance. Only two things can happen upon extracting materials, fail, or succeed. As your gathering skill increases, it is easier and faster to extract lower level materials.
For example as mentioned above, although Elyos Cleric and Asmodian Cleric would have almost the same skill sets, they might still have a completely different set of stigma skills which makes Mesos unique. First you must have acquired or activated the stigma system, which can only be done once you have reached level 20 and completed the Stigma tutorial quest.Once you have completed the stigma quest you would need Stigma Stones and Stigma Shards. Your first Stigma Stone and 300 Stigma Shards are given to you as rewards for the level 20 quest. Stigma stones can only be equipped with the help of a Stigma Master, who is located in Lyceum in Sanctum, and the National Assembly in Pandaemonium.You would also need a certain amount of Stigma Shards to equip the Stigma Stone. The amount of Stigma Shards are different depending on the skill being equipped.