Agriculture has a long tradition of developing experimental designs to establish rigorous field trials, particularly in plant breeding research. The overall design of the field trial is a key point to ensure the success of the experimental process. Although the importance of the principles of experimental design is widely recognised, they are not well understood and not well implemented in practice by some researchers. For example, randomisation is a fundamental principle in research, but it is not always fully respected. Using real yield data from grapevine field trials designed to quantify within-variety variability and fitting linear mixed models, this paper illustrates that incorrect conclusions about the research being conducted may be drawn if inappropriate randomisation is considered.