The use of Finite Element Modelling (FEM) techniques is the current pinnacle of mathematical techniques for representing the behavior of a structure. Of the many forms of FEM, the vast majority are stable and successful. However, the person using the techniques must make many decisions about what to include in to a structure and the value of parameters necessary for the modelling. A great many choices must be made.
As a result it is possible, even with a really good FEM, to obtain predictions of response that can be off by 100%.
If you are building an FEM, and you don’t calibrate it you could be accused of not following best practice, or worse of behaving unprofessionally.
The calibration exercise follows from a measurement of the dynamic response of a structure. Since this can be used to define the distribution of stiffness throughout a structure, it can be used to adjust the FEM, so that its predictions correspond with a measured response. Only under these circumstances is it realistic to use the FEM for predictions of response under different loading conditions.