Everyone makes mistakes, although usually it doesn't result in hundreds of websites going down. In our line of work typos can be one of the most common errors. Most of the time it is limited to an email or a text edit on a website but the other day an Amazon engineer's typo had a larger than expected impact on business around the world.
Read more about it here: http://money.cnn.com/2017/03/02/technology/amazon-s3-outage-human-error/index.html