In Oslo, Norway there is nothing stoping you from just entering a bus or tram without a ticket. There is, however, frequent ticket controls.

So one day on the bus from work, the driver anounced over the speakers, that since it was christmas and all she would like to advice us about a ticket control on the and a station 3 stops ahead.
About half the passangers rushed off on the next station.
As she started driving again she announced that there in fact was no control and thanked the rest of us for paying for tickets.