&gt;This is all around a much better system than FIFO. Of course LIFO is the fastest on average, but you want there to be a reasonable, predictable bound on how much time an individual can expect to wait.<p>Right, this is generally handled by how we (implicitly) judge queues, not by the average wait, but by the average <i>square</i> of the wait, and penalize extreme wait times that are concentrated on one person.<p>It&#x27;s why it&#x27;s better to have one line feed into multiple clerks rather than each clearly get their own line: because there&#x27;s the risk of some transaction taking a long time and screwing everyone in that line.<p>Single-queue avoids that by allowing people to be routed around that clerk. There&#x27;s no change in the average, but you&#x27;ve avoided major quadratic penalties.<p>It&#x27;s also the problem with LIFO: even if you could somehow stop people from leaving their early-entrance spot (!!) to re-enter for a better one, you&#x27;re still sticking a few people with horrible wait times, which good metrics penalize.