Poor measurement. If you can't measure it, you can't improve it. In terms of Lean, build your organization's supply chain function to support overall strategies, which can range from responsive to low cost, each strategy having its own type of metrics.
In today's world, it is easier to gather measurements through technology solutions, aided by bar-code scanning and RFID. But make sure you measure, compare, and benchmark the right things. One source of standardized supply chain metrics is the Supply Chain Operations Resource model, which features more than 150 individual measurements.