Computer Aided Engineering (CAE) Finite Element Method - Approach
How to Correlate Theory with the Real World 
The main problem with simulation is understanding how the virtual model interacts with it's real world counterpart.A datum, or benchmark must always be achieved so that this interaction can be understood. The aim of some analysis is to build a virtual model which resembles it's real world counterpart as closely as possible, yielding results which are as accurate as possible.
Whilst this is always desirable and sometimes ablsolutely necessary, it is not always achievable due to time and cost constraints. Weeks and months can be spent building perfect virtual models which can take days to solve. This does not usually further the cause of the project and ultimately does not yield a better product. Therefore, the analysis must always be viewed within the context of how it has been built to how it will be used in the real world.
A Pragmatic Approach
Due to complexity that can arise in creating a perfect virtual model which of course depends on the complexity of the problem being analysed, we only ever add complexity when it is really required. This holds true for the anlysis types that may be performed, as well as the materials data and boundary conditions applied.
Most problems in the real world are actaully quite complex once they have been thought through, these must be broken down into more simple problems achieving a datum set of results. Once the analysis used is accepted and well understood, a relative measure of performance is acheived in the simulation I.e if you make it better in the virtual word, then you make it better in the real word, even though the actual numbers yielded by the analysis may not be 100% correct. This isn't always required or necessary.