I used to work at a company that made network-attached storage appliances. Amazingly enough, one source of drive failures was the hot spare spinning up! The current draw during the spinup would cause a voltage dip on the power plane, which could lead to a read or write error on one of the neighbouring drives. Unfortunately, the most common cause of the hot spare spinning up was...another drive failing. So suddenly a second drive fails because of a read or write error.

The thing is, sometimes getting a read error doesn't actually mean the media is bad. There could have been some power fluctuation during the write, so the checksum doesn't match the data and the drive's controller returns a failure during the read. But if you rewrite that sector, it will be fixed (e.g. during an unconditional format).