Back when computers were the size of your garage, programmers often summarized a particular situation as “garbage in, garbage out.” It normally referred to either bad data or bad instructions that, when fed into a computer, led to worse results. For example, if the programmer’s client didn’t provide a precise description of the program’s objectives, the result might not be what was expected. Or, if the data being fed in was inaccurate, the results could be even worse.
The same comment applies to writing. No matter how much talent a writer may have, the results he or she will be able to produce are entirely dependent on the quality of information that’s available. If a client can’t express the objectives or parameters, there’s a good chance that what the writer does won’t meet expectations.