It might seem that once there is something wrong with your ceiling, for example water from upstairs has ruin it or something has broken of a chip from one of the tiles, this will be how it will look until you decide the to remodel the entire room again. Not quite true, repairing only the ceiling is not as hard as it sounds.
Of course the easiest ceiling to repair is the ones made out of different tiles as the only thing necessary is to replace the broken tile. A little bit of work and everything looks as good as it should.
Repairing ordinary ceilings is a little trickier task as it demands some basic knowledge about repair works. To start with, the pain on your ceiling has been ruined by something that just cannot be washed off; you need to repaint the ceiling. Of course you may try to paint only that one spot but probably it will not look as good as it did before. So maybe in this case the best way to repair your ceiling would be to repaint it all.
Secondly, somehow you have broken of a chip from the ceiling. Try to fill that spot and again repaint the ceiling.
The main advice to give about ceiling repair is if there are problems, contact a professional constructer and they can always help you out!