I think a line of people is actually a good representation of a progress bar.<br><br> You can see how many people are left in line, but you don't know how long each one will take. Say you're at a grocery store or a gas station; some people may only have a couple items, while others might have as much as can possibly fit into the cart. there's also plenty of unknown factors involved such as issues with the cash register. if it suddenly has an error and needs to be restarted, what would have taken a short time is now suddenly much longer. The cashier may go more slowly or quickly depending on what items are brought, a customer might start a lenghty small-talk conversation, or start an argument and request to see the manager, which would take far longer than it initally appeared.<br><br> The point is, you can see how many people are left in line, but you don't really know how long it will take. Having worked as a cashier at a gas station for a year and a half, I guarantee you all that plus many <b>many</b> additional factors have interrupted the smooth progress of a checkout line.,(reply>), Nice insight