I started my career as a high-pressure scientist at the University of Düsseldorf in 1981, where Karl took me as his first postdoc. Since I was supported by the Alexander-von-Humboldt fellowship, it was obligatory to get a minimum knowledge of German language. I spent four months at the Goethe Institute to learn German before starting my postdoc. The language course was so hard that, after four months, I almost lost my speaking skills of English. When I moved to Düsseldorf and was about to start work, Karl asked me if we communicate in English or German. I had no choice but to select German although my vocabulary was quite poor. Karl kindly accepted it, and we started our collaboration. The decision to use German as the daily communication tool was not bad, as I could talk to students in the lab and go for lunch together to the cafeteria every day. I gradually improved my knowledge of German. Karl frequently invited me to his home at weekends where I enjoyed wonderful dishes prepared by his wife Viktoria. At the university, we developed high-pressure techniques to measure reflectance spectra of metals with a diamond-anvil cell. Karl taught me the importance of correlations between electronic and structural properties of materials under pressure, which later became the guiding principle of my research. There are so many personal memories I recall with him, and I grieve his untimely passing. I recall his careful attitude toward experimental data and fruitful discussions based on physics. His contributions will remain a treasure for the high-pressure community.