Limit Break activates according to the number of Damage you receive (or more) and its Limit Break requirement value.
Example:
From the upcoming card from the Kai's TD06, Thunder Break Dragon's ability which is a Limit Break ability, there is Limit Break (4). Which means the effect only activates when you have 4 or more cards in your Damage Zone. So if you got less than that value, that effect does nothing and will not activate.
Discuss the concept of Limit Break and how you think it'll affect Vanguard in the near future.