OPs point is that your brain adapts to the level of caffeine you're ingesting. So if you're used to drinking coffee then you're basically at the same level of a

OPs point is that your brain adapts to the level of caffeine you're ingesting. So if you're used to drinking coffee then you're basically at the same level of alertness/functioning that you were before you first started drinking coffee (i.e. before it became habitual). The effect you notice from the first cup of coffee in the morning is really just the coffee counteracting the withdrawal you feel after ~6-8hrs of no caffeine.