Why do some people never get a hangover?

Yesterday I had a 70 cl bottle of 40 % abv. I remembered to drink 2-3 glasses of water, and take a rehydration tablet before going to bed, and I also had 2-3 glasses of water while drinking the rum. Today, like always, I don’t feel bad in any way. The only way I would feel bad the day after was if I was dehydrated.