How different variables interact with each other can happen in various ways. They can both contribute directly to the new variable or the could to turn the variable on and off, i.e., in the basic case one could model sales linearly like
With some coefficients in front of each variable. But maybe it needs some more complex dynamics with multiplicative effects
Such as if the brand awareness is 0 one can not sell anything and if the customers are unhappy one can not sell anything.
Also here one quickly realizes relying on a single model structure is foolish. So also here we need to actually try several different ways of doing it. That is why incorporating some high-level domain knowledge such as “NPS needs to have a positive effect on sales”, can help limit the potential combinations.