Comment by readthenotes1

Iirc, there is a quote from Barry Boehm, author of Software Engineering Economics, who said something in the effect of "I wish you hadn't persuaded me that requirements didn't change much in big military contracts"

They do change, especially if projects take years.

Not only do people tend not to read, or read well, there is a lot on inherent ambiguity in english--so even if not written stupidly there may be surprises.

"Requirements" changed on just about every project I was on. I remember once asking the business owner if he could simplify some requirements cuz they were really complicated to develop well, and he replied Certainly--he was trying to put out something he thought would be easy for us to build.