Isn’t even possible to prevent having a hangover the next day?

I’ve always been told that if you drink water while you’re drinking it’ll prevent a hangover which is what I did last night throughout the whole night. I’m usually just a get beer drunk type of person so it usually works. But last night I had beer and some shots. Thinking I would be alright but still woke up hungover even after drinking plenty of water throughout the night. Not as bad of a hangover but still hungover. So my question is what really causes a hangover or did I just simply drink too much and that’s why?