A paint that separates on the shelf. A plastic sheet that warps a week later. A rubber compound that just will not cure evenly, no matter what the operator tries.
Nobody talks about this enough: switching raw material suppliers is expensive, even when the switch looks free on paper. You test the new material. You adjust formulations. You run smaller batches to be safe.
Nobody budgets for bad talc. That's not how procurement works. You find a supplier, agree on a grade, lock in pricing, and assume the material will behave...