What is failstack?

[Quo]

Someone can explain to me what is failstack (a definition) and a simple way to build it?
Im near to finish the main quests and im trying to prepare me for the basic notions to upgrade a gear but i didnt really understand what is this failstack and how to see this value in game.

[Suzaku]

https://www.youtube.com/watch?v=1gsNLWVZpbs&feature=youtu.be

Enhancing can fail a lot, and that reduces item durability. To refill durability, you need copies of the item, which can be expensive. To avoid those costs, you intentionally fail enhancing crappy gear since it is cheaper to restore, and every failed attempt will increase the likelihood of you succeeding the next enhancement attempt.

So you build "failstacks" on crap gear, and when you think you're likely enough to succeed on an enhance, you make an attempt on the real piece that you want to upgrade.