YEP!there are so many variables that a cookie cutter "you should have this percentage of humidity" nonsense just won't work for everyone.. so it's best to pay attention to your hatches and adjust things until you have it down to a science
I think it is frustrating too because people feel like failures if a chick dies. So they are looking for fast answers rather than "get to know your equipment and conditions". We live in the instant microwave world now where answers are supposed to be at our fingertips as fast as we can type in the question.