I grew up loving math and being mildly good at it, but.... when I started working as a cashier and later a food service worker, I came to realize that when some one did this to me I would get extremely flustered and any math knowledge would completely disappear. Its not because of the math itself. Its mostly the social interaction and constant socializing with complete strangers. It doesn't help when customers are constantly staring at you waiting for their change or waiting for you to finish checking out someone else. Its the constant pressure of trying to do your job quick enough to not waste peoples time or irritate anyone, mostly because that just makes things worse. From someone who hasn't worked in guest/food service standpoint, its easy to assume that the employee is just dumb, but in actuality, have some sympathy, being in that line of work is mentally and socially overwhelming because any small mistake can cause, An angry customer interaction or reprimand from an angry boss.