Somewhere in school I got the backward idea that solving math problems is hard but that formulating them is easy. I don’t know if anybody ever said that to me. Maybe it was just implied by years of solving problems someone else had formulated.
A related wrong idea that I also picked up was that formulating math problems was not a mathematician’s responsibility. Someone, probably an engineer, would formulate the problem and hand it over to a mathematician. That happens occasionally, but that’s not how it usually works.
Formulating problems is hard, and it’s usually the applied mathematician’s responsibility, ideally with generous input from a domain area expert.
There are a lot of ways to turn a real world problem into a math problem, and maybe several of them would be adequate for the task at hand. Then you might as well choose the easiest one to understand and compute. Knowing several ways to formulate a problem increases your chances of find one approach that’s tractable. Particularly when you can determine what problem really needs to be solved, not just the problem you first see, you might give yourself more options for how to go about it.
Applied mathematicians don’t need to be an expert in every area of application, and of course cannot be. But they do need to meet clients half way (or more). They need to know something about the problem domain. They need to listen well and need to ask good questions. The questions help the mathematician get going, and they may also give the client something new to think about.