From a comment by Eric Loken at: http://andrewgelman.com/2015/04/28/whats-important-thing-statistics-thats-not-textbooks/
Every column of data has a label and numbers. Due to measurement issues, the numbers may have unobserved perturbations, and the label may or may not accurately stand for what the numbers actually represent. And from one model to the next, depending on the other covariates, the numbers actually represent can change. But the label sits on top of the column, and it sits in every summary table, and it all looks so clear cut that it is easy to take for granted that it is what says it is.