Primarily, a person that is put into the defense is provoked by their opposition. Meaning, that someone else is controlling their movement and this in turn can create loopholes into reading their defensive pattern. The best offense though is being random, but precise.
To be on the defense means to react to your enemies actions.
reactions can be caused by vision, or by thought.
A feint can ruin a perfect defense any day.
But timed actions against a force can cause a dramatic change on the situation; example: counters.
In the end, there is its ups and downs.
Styles can't be judged - only the men that use it.