The more innocuous the modification appears to be, the further its influence will extend and the more plans will have to be redrawn.
Second Law of Revision
You need to anticipate technical and business changes. Databases grow and need restructuring, and underlying system software changes. You should build applications with an architecture that can accommodate change.
Small, simple applications that deliver benefits quickly are preferable to monolithic applications, but the combination of small and very large applications should also provide the same benefit. You need to anticipate the growth of applications—organic growth is natural in successful applications, and you should allow for it.