You know what's funny? When I've been drinking coffee for so long that a cup of joe late at night no longer keeps me up. It just makes me really sleepy. "Oh, a cup of joe? Why, that's perfect for putting me to sleep!"
Even if I have another cup of joe, "Oh, this second cup doesn't do anything to keep me awake..." Bam! I'm asleep. A third cup of joe makes me go, "Why, this is barely keeping me up, let's try another one." Ahhh, the fourth one, "Man, this is finally keeping me up!"
It used to be that a cup of coffee or two was able to keep me up all night long. It doesn't anymore. Isn't that strange how I've built up a high tolerance level to caffeine?
When I was little, and had Coke before bed, I was jittery and couldn't sleep with all the sugar coursing through my veins. Now, at age 21, a 20 oz. Coke bottle does nothing to keep me awake. Oh, the irony!
You know what makes me perfectly sleepy? A cup of chai or mexican hot chocolate, yumm....