Whether you're standing in line at the supermarket or you're trying to navigate through traffic, it seems like the other line is always moving faster than yours. BBC Future explains that this is partially due to a phenomenon known as 'illusory correlation'.
Illusory correlation exists to help us make quick decisions based on limited information without doing a lot of mental maths. In effect, we compare two things as if they were similar even when they're not, such as two lines at the supermarket. BBC Future explains it like so:
So here we have a mechanism which might explain my queuing woes. The other lanes or queues moving faster is one salient event, and my intuition wrongly associates it with the most salient thing in my environment — me. What, after all, is more important to my world than me. Which brings me back to the universe-victim theory. When my lane is moving along I'm focusing on where I'm going, ignoring the traffic I'm overtaking. When my lane is stuck I'm thinking about me and my hard luck, looking at the other lane. No wonder the association between me and being overtaken sticks in memory more.
This distorting influence of memory on our judgements lies behind many my feelings of victimisation. In some situations there is a real bias. You really do spend more time being overtaken in traffic than you do overtaking, for example, because the overtaking happens faster. And the smoke really does tend follow you around the campfire, because wherever you sit creates a warm up-draught that the smoke fills.
But on top of all of these is a mind that over-exaggerates our own importance, giving each of us the false impression that we are more important in how events work out than we really are.
Essentially, we tend to think we're more important than we are, and that's part of the reason why we hate standing in lines to begin with. If nothing else, a better understanding of the psychology behind why you think other lines move faster than yours will help you deal with it a little better.