The Importance of Understanding the Latent Variable

Sometimes the best latent variable is no latent variable at all. I don't believe this poly substance variable exists as a valid and reliable measure of substance use, but it sure represents something that I'm interested in. And I'm going to put that in knowing that maybe that's really a causal indicator factor and I'm treating it as an effect indicator. But I've got a longer con that I'm working on. It takes us back to first principles. What is the construct? What do you believe to exist? And how are you assigning numerical values to that?"