A Small Mistake Behind The Bar

I was working behind the bar last night when I accidentally mixed up two customers' orders. One had requested a classic margarita while the other wanted an espresso martini, but due to the rush and my inattention, I served them swapped drinks. They both seemed confused for a moment, but after a quick apology and explanation, they laughed it off. Yet, as someone who prides myself on precision and attention to detail, this mishap keeps nagging at me, I need to figure out what led to such an uncharacteristic mistake.