Why focus plateaus while jitter keeps climbing
Stimulant benefit and stimulant cost do not scale together. Cognitive measures such as alertness and reaction time tend to improve with a stimulant up to a moderate dose and then flatten, because the receptors and arousal systems involved saturate. Unwanted effects, jitteriness, raised heart rate, and anxiety, tend to rise more steadily with dose because they track sympathetic overactivation rather than the cognitive sweet spot.
The diagram shows these as two separate curves: a focus benefit that bends over into a plateau, and a jitter line that keeps climbing. The practical reading is that pushing the dose past the plateau buys little extra benefit while still adding cost.
Finding the personal peak
The most useful dose sits near where the focus curve flattens but before jitter becomes limiting. That point differs widely between people because of genetics (notably caffeine-metabolising CYP1A2 variants), habituation, body size, and time of day. There is no single optimum, which is why the diagram emphasises an individual peak rather than a universal number.
Tolerance also shifts the curves over time. This is general educational information, not medical advice; people with anxiety, arrhythmia, or high blood pressure should be especially cautious and consult a qualified professional before dosing stimulants.