2 Mixed models series: Two stage random effects formulation

When I barely knew anything about mixed models I was struggling with how to specify a specific model in the software I was using and a professor told me to just "picture" what the variance structure looked like and use that "picture" to set up the model. Well...nobody ever gave me a mixed models paintbrush to make such a picture. I have found the two-stage random effects formulation helps me understand what the mixed model is doing and helps me build the picture I need for setting up the model. It is a very useful learning tool albeit not 100% perfect for explaining all mixed models.