"The three o'clock slump is just how afternoons are"

You may accept all this about the morning and still feel that the afternoon is different. Everyone flags after lunch. It's biology. The coffee at three is just working with the grain of the day.

There's something in this, and I want to separate the two things that happen at three.

One is real and has nothing to do with caffeine. Most people have a dip in alertness in the early afternoon. It's part of the daily rhythm, and it's why some cultures built a rest into that hour. If you didn't drink coffee, you'd still notice that two to three is not your sharpest time. That's the slump's first cause, and no cup will fix it, because it isn't a shortfall.

The other is the shortfall. Go back to the second Bristol experiment. The regular drinkers who were kept off caffeine got steadily worse from the morning into the afternoon, and the worst effects showed in the later tests. Their morning cups had worn off. That's the same thing that happens to you every day between half past nine and three. The second cup was at half past nine. By three its effect is mostly gone, and you're sliding towards the shortfall, at the same hour as the natural dip. The two arrive together, and the result is the fog on the paragraph.

So the three o'clock slump, for a regular drinker, is a natural dip with a withdrawal low on top of it. The coffee at three removes the withdrawal part. It leaves the natural part, which is why the pick-up at three never feels as complete as the one at seven.

This matters for what to do. If the afternoon low were pure biology, coffee would be a reasonable response to it and the book would have little to say. But a good part of it is a low that the morning cups made. Reduce the morning cups over a couple of weeks, as chapter 18 describes, and the withdrawal part of the slump shrinks, because there's less to withdraw from. What's left is the natural dip, and that's a smaller, gentler thing that chapter 19 will show you how to handle without a kettle.

I'd also ask you to notice the timing of the three o'clock cup in relation to the night. If you go to bed at eleven, three is eight hours before. Chapter 7 will look at how far a cup that far out reaches.