Why is it not recommended to use RAID 5 for a log file?

While reading SQL Server Query Performance Tuning written by Grant Fritchey, I found it difficult to understand the following part: ***avoid RAID 5 for t-logs because, for every write request, RAID 5 disk arrays incur twice the number of disk I/Os compared to RAID 1 or RAID 10.*** I know that RAID 5 differentiate from other RAIDs with its parity feature. It means that if some of the drives fails, then it is possible to recover lost data from the other drives. I want to understand why it is not recommended to use RAID 5 for a transaction log file. Explanation in the book was not enough for me to get it. Maybe someone could explain it to me or provide a good article.