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:
I should point out EXTRA care should be considered when handling recordable CD's and DVD's... Unfortunately, the blank media manufacturers have gotten bad publicity lately, making defective recordable media (unreadable media after only a few weeks for example). To make matters worse, even reputable manufacturers are making their discs in different plants as of recently that make unreliable media (like CMC corporation in Taiwan, the largest of about 11 media manufacturing plants in the world). To lower production costs of course, these companies would be Verbatim, Memorex and a few others (things are continously changing these days with the blank media corporations, this information may not be up to date). Even worse than that, some "fake" media have surfaced around and have been packaged with falsified media codes (not just the outside packaging but content prerecorded on every recordable disc) from reputable media brands like TDK or Maxell for example (rarely you'll find these through CD/DVD spindles). It's best to stick with the brands you know that come from that company (only TDK and Maxell will package their discs in cases for example). Sometimes you never really expect what you buy when it comes to blank media.
It's best to buy media from a store that has a good return policy. There are FEW reputable online places as well (like rima.com), but they are only retailers, they don't make the discs of course.