When people change things in their lives – jobs, houses, marital status, whatever – it is often customary to send cards saying things like ‘congratulations’ or ‘good luck in your new job’.
It randomly occurred to me this afternoon that nobody ever sends cards like this when things are staying the same. How about sending a ‘good luck staying in your current job’ card to an employee of a company whose stocks have just plummeted? Or ‘congratulations on staying in your current job’ a month or two later, after the mass redundancies have finished? ‘Good luck in your old home’ if it's slowly falling apart or local property prices are falling? ‘Well done for still having all your limbs intact’, sent at irregular intervals to someone who does particularly extreme sports? Lack of change is sometimes just as much of a risk or an achievement as change, and can perfectly well merit celebration.
I suppose you could see birthday cards as congratulating the recipient on still being alive, and wedding anniversary cards likewise on still being married; but I think those lack ambition. There must be a fortune to be made in non-event greetings cards if you're willing to push the cynicism just a bit further :-)