I realize that in all my life I have not become accustomed to thinking about weights and measures in the metric system without thinking about the units in the U.S. standard or traditional system. This is much like learning a foreign language but having to translate in your head before speaking or understanding. I think this is because I learned about weights and measures as a child with the traditional system, so I have established mental reference points in my memory.
I was recently thinking about temperature. What would it take for me to understand Celsius so that I don't have to convert it mentally? Is 27 degrees in Celsius warm or cool? It is easy to talk about temperature in Fahrenheit, and I think I have memories of feelings or even specific things associated with different numbers: