That's why a year ago, when I was experimenting with the effects of caffeine on myself, I switched between regular coffee, decaff, and coffee with caffeine pill

That's why a year ago, when I was experimenting with the effects of caffeine on myself, I switched between regular coffee, decaff, and coffee with caffeine pills. And the acclimatization effects is why I used each for a full week before switching. It turns out that caffeine has no detectable effects on me at all; I already knew it didn't have much effect, that's why I used such an elaborate trial.