Why do Dijon mustard & American (yellow) mustard taste nothing alike? Which one do you prefer & why?

I’ve never understood why Dijon mustard & yellow mustard are so different. I remember the first time I tried Dijon mustard; I thought I was eating paint thinner!! (Needless to say, I haven’t developed a taste for Dijon mustard yet.)
Thanks for the info so far. I was wondering what spice or ingredient in Dijon mustard [...]