The type of change whose effects ripple throughout a system, in unpredictable (but hopefully beneficial) ways.  

One situation where this invariably happens is where one finally groks some concept (objects, functional, event driven, small talk, etc.).  One small improvement leads to the discovery of a new problem, except that its solution is discovered to be an expansion of the improvement, which in turn uncovers more opportunities.

The 'problems' which are discovered turn out to be workarounds, put in place under the misunderstanding that such workarounds are how the concept is ''supposed'' to work.  The application of the solution ends up uncovering other workarounds, which were borrowed from other contexts, and so on and so forth, until the entire structure ends up being revamped... in an extreme case, it may not even look like it's solving the same problem any more(think 'WhatIsAnAdvancer').  Really, what happened is that the essence of the problem, the essence of the concept, has been uncovered.
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See also: SeedCrystal

AhaMoment