Think bad power supply, mains spike, cooling failure, fire, flood .....
If you need raid, you also need a separate copy in a separate location.
In contrast, I lose 5-10% of the spinning HDDs I care about every year.
Jeff Atwood made an interesting post on that very subject a while back, though:
http://www.codinghorror.com/blog/2011/05/the-hot-crazy-solid...
Every spot in our solar system is susceptible to some unrecoverable disaster. If you don't want to lose your data, you have to have copies in more than one physical location.
Seriously, I didn't say he was wrong in theory, but focusing so much attention on the highly unlikely to the detriment of the exceedingly common is a drastic distortion of the issue, and a cost/benefit analysis skewed in either direction can have costly repercussions.