You may be a reference librarian if...

...if you've ever helped someone make a reservation for someone to use one of the internet computers.

And they've then complained that they can't wait the 4 minutes until the computer will be available.  They assure you that all they want to do is check their email really quickly, they only need the computer for a couple of minutes, etc., etc.

Then you have to explain that all of the other computers are in use or assigned other reservations, and, really, if they wait 2 more minutes, they can have the computer.

Grudgingly, the person agrees to wait.  So, a mere 120 seconds later, the person is able to sign in to the computer.

And then, 20 minutes later, you realize that the same person is playing Farmville on Facebook.