In the five element destructive cycle the elements control each other as shown in the diagram on the right.
In this cycle, Fire controls Metal which controls Wood which controls Earth which controls Water which in turn controls Fire.
Again try not to think of it as one element destroying another. Instead, think of it as one energy influencing another in a controlling manner!
The five elements destructive cycle is not so intuitive but you can easily remember it like this. Think of a metal axe. You use it to chop down a tree hence Metal destroy Wood. Think of a large tree. It extract water and minerals from the earth to grow hence Wood destroy Earth.
When a river burst its bank, you use bags of sand (earth) to stop the overflow hence Earth controls Water. You can extingush fire with water hence Water destroy Fire. Finally as in a iron foundry, you use fire to metal. Hence Fire destroy Metal. See, it is easy!
Again, how do we apply this in Feng Shui?
Classical Feng Shui systems nomally divide a house into nine sectors called the Nine Palaces. Let's say the a particular sector has a lot of fire and it makes the sector inauspicious.
Normally you would use earth, which you will learnt later, to reduce fire. But as you might already guess it is not a very effective method. You need a lot of earth to put out fire. Think of throwing sand at a fire to stop it from burning.
A more effective way is to use water to put out the fire! This is an example of five elements destructive cycle or controlling cycle in action.