Schlechtriem, Peter (ed.), English Commentary on the UN Convention on the International Sale of Goods (CISG), Comment on Art. 79 by Hans Stoll, Oxford 1998

6" The promisor is, therefore, basically liable for any objective failure to perform, regardles of the reasons for the failure. The promisor is not exempted merely by proving that the failure to perform was not due to his fault.25 Only proof that the failure to perform was due to the effect of an impediment outside his control can relieve him. Article 79 makes the inability to control a risk a general principle of exemption.

25Bianca/Bonell/Tallon, Art 79, note 1.1; Herber/Czerwenka, Art 79, para 2; Herber, UNCITRAL-Übereinkommen, p 47; Schlechtriem, JZ 1988, 1037, 1047; on ULIS, von Caemmerer, AcP 178 (1978), pp 121, 145.