I've seen other people handle CDs and DVDs as if they were indestructible. I take great care to handle mine properly, keeping them from in climate-controlled conditions, protected from temperature extremes.

Here's an article about someone who didn't take necessary precautions, and found that some 15 to 20% of his 2,000-CD collection no longer played properly:

http://tech.tbo.com/tech/MGARCOIKXTD.html