Guideline: CompartmentalizationPart of: Technology Security Guidelines
Overview: Building a set of Guidelines for Security and Privacy
A striking analogy of this principle is that of a ship. Every (larger) ship is built in compartments. When a breach in the outer-wall has happened, the compartments makes sure that the flooding won't impact the entire ship. This principle can and should applied in technology also.
Compartmentalization can be applied on multiple levels within technology and you can do it as extreme as you want. Remember that there is a trade-off when it comes to compartmentalization of systems and environments. Because every transaction that needs to crossover to another compartment needs to be validated before it is allowed. It will require maintenance (which could be automated to some degree), and it will take for sure resources like processing power.
More information from Wikipedia about Compartmentalization.