I assume that Planck was trying to refer to the process of abstraction in his lecture. And it's true that theoretical physics does operate at a very high level of abstraction. That's one reason why theoretical physics is so often joined-at-the-hip with mathematics. It isn't as true for experimental physics though. Interpreting Planck's remark too aggressively would eliminate all the empirical elements, such as experiment and observation, from physics. I'm sure that Planck didn't want to suggest that anyone do that.