Seeing through: what is hidden behind simple requirements

Let's assume a multicomponent system: web interfaces, mobile and desktop applications, a cloud that provides information exchange, integrations with external systems, several REST API implementations. The architecture of the application is similar to a complex molecule, even without diving into depth.

There are simple demands such as adding a field to a document. It would seem that everything is very easy! The user work script and logic have changed to a slight extent, there are small edits in the database. The task is quickly sent to development. But unexpectedly, a "complex molecule" can remind of its versatility and begin to influence.

Sometimes, in the absence of system analysis, even for a simple requirement, more and more errors may appear with each iteration of development and testing. Sound familiar?
 
How to defeat influence on everything? Try to learn to see right through when designing systems.