Have you ever gone to a convenience store during rush hour, seen three cashiers open, and your primitive instinct immediately told you to run to the line with the fewest people? Then five minutes later you regretted it because the longer line next to you finished first?

I used to experience this a lot when I was a freshman, until I learned Queue Theory in my applied math class. This knowledge completely changed how I see the world, especially when I am hungry and want to pay for my noodles quickly.

The problem is, humans are cognitively biased. We only count N or the number of people in front of us. But waiting time is not just about the number of people, it is also about service time. This is what makes a short queue an illusion.

Imagine this, queue A only has one person, but they are buying phone credit, paying their electricity bill with coins, and topping up their e-wallet on a bad connection. Their service time could easily be 10 minutes. Meanwhile, queue B has four guys, but they are all just buying cigarettes and bottled water. The service time per person is a minute max. The total for queue B is only 4 minutes.

This is where the error in our brain's queue-searching algorithm lies. We do not include the transaction complexity variable.

According to Queue Theory, there is a model called M/M/1. It stands for Markovian Arrival, Markovian Service, 1 Server. Basically, customer arrival and service times are random (Poisson or Exponentially distributed). If there are multiple cashiers, it becomes M/M/c.

Now, the most optimal strategy for a convenience store (and unfortunately the most rarely implemented here) is a single queue multi-server, like in a bank. Everyone waits in one long line, then goes to whichever cashier is open. This system is mathematically proven to lower average wait times and prevent frustration from picking the wrong line.

But since convenience stores use separate parallel queue systems, you have to be smart about scanning the situation before putting your shopping basket down.

How do you hack the checkout line?

First, do not look at the number of people, look at what they are buying. If there is a mother with two full carts of monthly groceries, avoid it. If there is a guy pulling out a stack of water bills, run.

Second, pay attention to the type of cashier. A cashier who is still training or looking confused trying to find the barcode has a low service rate. You are better off lining up at the senior cashier whose hands are like an automated machine scanning items without looking at the screen.

Third, do not keep switching lines. This is a common disease. You are already in line A, then you see B moving fast, so you switch to B. Then when it is your turn in B, the cashier suddenly runs out of change and has to wait for their coworker to get coins from the back. You wasted transition time and you started from zero again.

In conclusion, probability is always around us. Stop relying purely on instinct. Use simple data analysis before making a decision. Your life will be much more efficient and you will not get emotional just because you are waiting for someone paying their motorcycle installment with coins.