Someone explain why this keeps happening

It feels like at my job, I could be standing around doing just about nothing for 5 or so minutes just waiting for customers, so then I decide to do something else (refilling stuff, throwing things out, replacing sanitizer, getting tubs, etc. etc.), THEN someone shows up. It's been happening to me constantly and it drives me crazy, doubly so when they have the nerve to interrupt me instead of just waiting for me to be finished. Props to the customers who DO decide to wait until I'm done though. It's like people know when I'm about to do something actually important and just suddenly have a craving for ice cream/milkshakes.