Well, you put up with something for literally years (an annoying green moon-like blob in the centre of the screen when I'm watching films on my Hitachi PJ-TX100 projector) and it's really annoying sometimes, especially in dark films (like Moon for example) but you try to grit your teeth and not make a fuss like your parents taught you, and then one day you wake up and think "Why am I putting up with this? This is the age of the internet!" And after about 10 minutes of research you find the answer (here). You spend £20 on a compressed air thingy (quite a lot, but a lot cheaper than a new projector) carefully squirt it into the correct opening and bingo! It doesn't work. But you try again and again and finally get a torch so you can see what you're doing and - aaaah - it works. Bliss. You've no idea how nice it feels to watch a film without the green blob.
Isn't the internet great?