What is the golden rule of inventory management?

The golden rule of inventory management: never let your records drift from reality — every other inventory decision is only as good as your stock accuracy. Forecasts, reorder points, promises to customers, purchase budgets: all of them silently assume the number in the system matches the number on the shelf. When accuracy slips (untracked damage, unrecorded samples, mis-picks), every downstream decision inherits the error.

The supporting rules follow from it: record movements when they happen, not later (later means never); make it easy to do the right thing (scanning beats typing); count continuously in small slices (cycle counts) instead of one heroic annual count; and investigate discrepancies instead of just adjusting them away — a recurring shrink pattern is information.

Get accuracy right and the popular frameworks (ABC, 80/20, JIT) actually work. Skip it and they're decoration.