The most shocking thing for me was the realization that frequency and wavelength are kind of dual forms. Ofcourse, every concept and thing that comes into existence does so only in the context of it's opposite or dual form. But recognizing that form is genius. 3b1b video goes a bit deeper.
Also a related fact is that the rate of change of a sine wave is itself shifted by pi/2, while the exponential curves need no shifting. I'm not a professional in these matters, but I guess there is a deeper connection between the rate of change and the static world.