Anyone who's been to an airport recently will notice that the major airlines have installed those self check-in terminals. The idea is that you swipe your credit card so they know who you are and it spits out your boarding pass. Sometimes it doesn't work, so you have to enter another piece of information, like your ticket number. Sometimes that still doesn't work so you enter some other piece of information like the flight number. And if that doesn't uniquely identify you to the system, you're stuck standing in line waiting for a ticket agent to issue you a boarding pass.
So, airlines, if you're going to do this, you need to make sure it's much more robust and that it works for everyone. There's not much point in implementing the check-in terminals if it's going to result in long lines of hundreds of people who end up having to see the one or two ticket agents you only have on duty because you've reduced staffing (because the check-in terminals are supposed to be "more efficient").