Because the chain is so long and complex, with opaque supply channels, unknown practices of individual traders, and numerous intermediate stages, monitoring can usually only take place in the final links of the chain.

Sources: [nager-it.de](https://www.nager-it.de/static/pdf/lieferkette.pdf "Öffnet externen Link in neuem Fenster"), [bgr.de](https://www.bgr.bund.de/DE/Themen/Min_rohstoffe/Downloads/Rohsit-2012.pdf? "Öffnet externen Link in neuem Fenster"), [destatis.de ](https://www.destatis.de/DE/ZahlenFakten/GesellschaftStaat/ "Öffnet externen Link in neuem Fenster")