Chaos Theory states that small changes in a complex system can change rapidly and unpredictably.
ex. you are sitting on a shoreline and you see in the distance a storm coming slowly closer. It's heading right for you. You see lightning flash out across the water and the waves come towards the shore at an increasingly violent rate. At this point the storm has two options. One would be that the storm would race straight towards shore and continue it's rampage there which would seem to be the logical choice. Instead however, before the storm reaches land it changes it's direction and shoots down the shoreline instead. This is the chaos effect, you cannot predict how the storm will react because it is a large complex system dependent on very small changes that it encounters in the natural environment.