So eventually the caffeine breaks down, lets go of the receptors and all that adenosine that has been waiting and building up latches on and the drowsy feeling

So eventually the caffeine breaks down, lets go of the receptors and all that adenosine that has been waiting and building up latches on and the drowsy feeling comes back – sometimes all at once. So, the debt you owe the caffeine always eventually needs to be repaid, and the only real way to repay it is to sleep. Since many people also have trouble falling asleep this seems like a win-win if you can the timing right.