I'm not sure if it's clear, but in the elevator lobby it's not up or down buttons, but an electronic screen with buttons for each floor. After you push the button for your floor, the display will tell you which of the elevators to wait for (e.g. elevator A, B, C, or D). Then you wait for your assigned elevator - you don't go into any other elevators that might come first - 98% of the time it won't go to the floor you want to go to. Once your elevator comes you get in and that's it, there's no floor buttons inside the elevator to push[1]. It messes a lot of the food delivery guys up the first time they encounter it.
Another feature is that you can do a "group call" - if you have a lot of people over you can use group call to get an elevator dedicated just for you and your party (and yes it can be easily abused, but I've rarely seen it happen).
What happens is that you push the floor you want to go to, wait over x minutes, get impatient and push again. Now, it won't necessary assign you a different elevator right away, but you wait another x minutes, get impatient and push again, and wait and push, and wait and push, etc. Eventually, you end up calling up all the elevators - and this is not just "you", but everyone else waiting for the elevators in the entire building - which obviously bogs the system down even more. Usually this system works alright, but if an elevator breaks down, or even if one is booked for delivery, the algorithm is pretty crap and it bogs down. When two elevators are down, it really can take > 20mins to wait for an elevator.
That's why I mentioned that when I'm trying to go to ground and it's taking a long time, I'll push to go up a floor and ride the elevator up, as it'll eventually go down to ground again. And this is faster than waiting for the "official" down elevator that was originally assigned. It's stopping the frustration/impatience and temptation to push the damn button again that's key.
[1] there are buttons inside the elevators actually, but they are locked behind a panel. The panels are only unlocked when you've booked it for delivery (and I guess for emergency personnel, or if the display is broken or something).