Travails of queuing up

What's worse than being stuck in a queue, is reaching the counter to know that the product for which you stood in the queue, is not available.

Happened to me at the medical store at St. John's hospital. After being stuck in the queue for close to twenty minutes, I reached the counter to know that the prescribed drug was out of stock. Now, how irritating is that?

If you ask a consumer to queue up, one, ensure that he spends as less time as possible in the queue, and two provide him with whatever he queued up for.