Assumptions you can check
Every model is built in a spreadsheet your team can open. Demand, margin, lead time, return rate and storage cost each sit in a visible cell with a note on where the figure came from. When a figure is a guess, it is marked as one. We would rather show a model that can be argued with than a polished forecast nobody can test.
When actual results differ from the model, we look at which assumption was wrong, update it and record the change. Over a few cycles the model becomes a record of what your business has learned.

