Self Check-out or IQ Test?

Living next to Walmart, I am often faced with a dilemma: Stand behind 20 people in the regular check-out lane or stand behind 5 people in the self-check out lane. Calculating the time it will take to use the regular lane is easy; I just have to appraise the competence of the Walmart employee. Gauging how long the self check-out will take is a little more complicated: I have to determine about how long each individual shopper will take. But even though my mind goes through this calculus and arrives at the conclusion that the regular will be faster due to the lower number of unknown variables, the simple visual or 20 customers compared to 5 leads me to throw practicality and experience to the wind and jump in the self check-out line.
Generally, after about five minutes (in which time the same person is still trying to scan the same item or find the code for a cucumber) I realize that I gambled and lost. Not wanting to have to start the wait over by jumping lanes, I resign myself to inevitable long wait and make myself comfortable. I usually pass the time by trying to guess how long each shopper will take to check himself/herself out. This eventually leads to me guessing the IQ of each shopper based on how efficiently they can use the machine. After watching countless people use these self checkers, I have come to the conclusion that I am surrounded by morons: they grap the box of generic mac n' cheese; slowly run the wrong side over the scanner; stand there perplexed that there wasn't a beep; examine the box; find the bar code; slide the box across the scanner again; hear the beep; stop; check to see what just got added to the screen; because they took so long reading the screen, the machine is now saying that they removed something from the bagging area; so they hit the "Skip baggin" button, but then place the box in a bag, which causes the machine to scream "There is something unexpected in the bagging area;" then the Walmart employee comes over and enters her code in . . . you get the idea.


Fifteen minutes later that genius is finally done and it is time for the next Mensa member to take her turn. Now, I know Walmart isn't know for having the brightest clientel, but you think that things wouldn't be so bad in a college town. Can someone please explain to me why otherwise intelligent people can't use a simple machine? Although, I guess the fact that I keep getting in the self check-out line says something about my own IQ.