Mistaken Order

So last night at work, I made the dumbest mistake. A customer asked for a Manhattan with extra bitters and no cherry, and instead of just adding more Angostura to their drink, I accidentally put in way too much extra bitter syrup. The guy was already pretty tipsy and couldn't taste the difference anyway. But it got me thinking, why do we sometimes overlook simple instructions and complicate things? It's like my brain decides to go on vacation right when you need it most.