Which grocery checkout line should I pick?

Always pick the longest line. If you pick the shortest one, the checkout gods will conspire to put some obstacle in your way. The person ahead of you will have a purseful of manufacture's coupons or eight separate food assistance vouchers that must be handled as individual transactions. If you choose the longest one, you'll be appeasing the checkout gods by sacrificing yourself in advance. It will take the same amount of time either way, but the reason for your delay in a long line is at least obvious and expected.

Please make note of the fact that this rule of thumb applies only to you. Other people are allowed to jump into the short line and be out in a matter of seconds, but you must resist the urge at all costs. If you move to the short line, the cash register will lock up.