It's not "mistake" singular, it's actually mistakes. The first mistake is the $500 million rover is fried. The second mistake is believing the first mistake.

It's not "mistake" singular, it's actually mistakes. The first mistake is the $500 million rover is fried. The second mistake is believing the first mistake. (or put another way, the first mistake cost $500 million, the second mistake which they didn't realise at the time, saved $500 million) But you can't explain the second mistake without first explaining the first mistake, hence the title.