Thanks to my wife I've come to learn that I probably have ADHD. I never would have realized it on my own, but it's so obvious when someone points it out. If she has an extra cup of coffee she is buzzing and shaking for hours, whereas its basically a sedative to me. I can drink a whole pot and still pass out on the couch for a mid day nap lol.
I'm not sure that this is universal. I've been diagnosed with ADHD, and ADHD drugs do help me focus. But I'm super sensitive to caffeine, too. If I have even a can of soda at night, I can't fall asleep.