The worldwide COVID-19 outbreak has impacted on the domestic and international supply chains of Japanese firms. In particular, internationalized production has been blamed for working as a propagation mechanism in the worldwide spread of negative shocks. Todo and Inoue (2021) extensively review existing studies that have examined the shock propagation through supply chains and what characteristics of supply chains enhance or mitigate the propagation, in the cases of previous crises and the current COVID-19 crisis. Based on their literature review and the data observations on the current characteristics of Japan's supply chains, Todo and Inoue highlight the need for more geographical diversification in suppliers and clients of Japanese firms to build robust and resilient supply chains and improve the firms' performance.

In the face of the COVID-19 crisis, there has arisen a renewed argument that shorter and simpler supply chains and reshoring production back to the domestic economy would be less vulnerable to shocks. Against this kind of turning-inward policy argument, Todo and Inoue emphasize the potential benefits from supplier substitutability and international knowledge diffusion through geographically diversified supply chains, which is quite meaningful.

Nevertheless, I suspect that geographical diversification of trading partners is not the only way to build a resilient supply chain. A firm's optimal strategy for resilience might not coincide with that for robustness. The concept of system resilience was originated in the ecology literature and was applied to the risk management literature. In the light of supply chain management, resilience can be the ability to resume normal operations after an acceptable period of disruption, while robustness is the ability to maintain operations amid a crisis (Miroudot, 2020).

Supplier substitutability appears to be a key to achieving robustness. Maintaining geographically diversified suppliers or alternative locations of production would enable firms to withstand a location-specific supply shock, which leads to the greater robustness. To improve resilience, on the other hand, a firm might rather prefer to develop a long-term relationship with a single supplier, or a handful of suppliers such as keiretsu, as discussed in Miroudot (2020), for example. Maintaining a less diversified but close relationship would enable a firm to receive investment or support from the partner for minimizing the time and cost of disrupted operations and facilitating recovery from the disruption, which leads to the greater resilience.

Indeed, Todo and Inoue (2021) touch on the possibility that the keiretsu-type relationships would help improve resilience in the case of knowledge-intensive goods. It would be insightful if Todo and Inoue could elaborate on the implications of geographical diversification for the robustness and resilience of supply chains with more careful consideration of the two related but distinct concepts.

In addition, I am skeptical of Todo and Inoue's policy suggestion that the Japanese government should intervene to promote the geographical diversification of suppliers. The diversification of suppliers is not necessarily an optimal strategy from the firm's perspective, depending on whether the firm prioritizes the robustness or resilience of supply chain as well as on the firm's product or industry characteristics. Even if the current level of diversification is less than the optimal level as argued by Todo and Inoue, a government inevitably faces implementational challenges on the intervention and possibly distorts a firm's decision on production locations and sourcing patterns, which could force the choice of an inefficient location. Rather, a government should devote itself to ensuring an environment where firms can build and develop domestic and international supply chains as they need, as a basis for economic growth, which brings greater efficiency, expands the production frontier, and facilitates technology and knowledge diffusion and spillovers.

Last but not least, Todo and Inoue's literature review and accompanying discussion focus on the effects on supply chains of supply shocks such as natural disasters. When thinking of the robustness and resilience against the current COVID-19 spread, however, we should be aware that COVID-19 generated both supply and demand shocks. As a result of social-distancing policies, industries relying on the movement of people, such as hotels, restaurants, and passenger transport services, have been impacted greatly through the fall in domestic final demand. It would be worth discussing the robustness and resilience of supply chains not only against supply shocks but also against demand shocks. Does the shock propagation mechanism of supply chains matter to a similar degree and work in a similar way in the case of demand shocks as in supply shocks? The firm's strategy for robustness or resilience of concern also would depend on the source of shocks. Todo and Inoue could discuss on this further.

全球范围内的 COVID-19 爆发已经影响了日本公司的国内和国际供应链。特别是，国际化生产被指责为负面冲击在全球范围内传播的传播机制。Todo 和 Inoue（2021 年）) 广泛回顾现有研究，这些研究检查了冲击在供应链中的传播以及供应链的哪些特征会增强或减轻传播，在以前的危机和当前的 COVID-19 危机的情况下。根据他们的文献回顾和对日本供应链当前特征的数据观察，Todo 和 Inoue 强调需要在日本公司的供应商和客户中进行更多的地域多元化，以建立强大和有弹性的供应链并提高公司的绩效。

面对 COVID-19 危机，人们重新提出了一种观点，即更短、更简单的供应链以及将生产回流到国内经济将不太容易受到冲击。针对这种转向内向的政策论点，Todo 和 Inoue 强调了供应商可替代性和通过地理多元化供应链进行国际知识传播的潜在好处，这是非常有意义的。

尽管如此，我怀疑贸易伙伴的地域多元化并不是建立弹性供应链的唯一途径。公司的最佳弹性策略可能与稳健性策略不一致。系统弹性的概念起源于生态学文献，并应用于风险管理文献。根据供应链管理，弹性可以是在可接受的中断期后恢复正常运营的能力，而稳健性是在危机中维持运营的能力（Miroudot，  2020 年）。

供应商可替代性似乎是实现稳健性的关键。保持地理上多元化的供应商或替代生产地点将使公司能够承受特定地点的供应冲击，从而带来更大的稳健性。另一方面，为了提高弹性，公司可能更愿意与单个供应商或少数供应商（如 Miroudot（2020）中讨论的那样）建立长期关系。保持不那么多元化但密切的关系将使公司能够从合作伙伴那里获得投资或支持，以最大限度地减少中断运营的时间和成本，并促进从中断中恢复，从而提高弹性。

事实上，Todo 和 Inoue（2021 年）谈到了在知识密集型商品的情况下，keiretsu 类型的关系将有助于提高弹性的可能性。如果 Todo 和 Inoue 能够通过更仔细地考虑两个相关但不同的概念来详细说明地理多元化对供应链稳健性和弹性的影响，那将是有见地的。

另外，我对Todo和Inoue提出的日本政府应该干预以促进供应商地域多元化的政策建议持怀疑态度。从公司的角度来看，供应商多元化不一定是最佳策略，这取决于公司是否优先考虑供应链的稳健性或弹​​性，以及公司的产品或行业特征。即使目前的多元化水平低于 Todo 和 Inoue 所主张的最佳水平，政府也不可避免地面临干预的实施挑战，并可能扭曲公司对生产地点和采购模式的决定，这可能迫使选择低效率地点。相当，

最后但并非最不重要的是，Todo 和 Inoue 的文献综述和随附的讨论重点关注自然灾害等供应冲击对供应链的影响。然而，在考虑对当前 COVID-19 传播的稳健性和弹性时，我们应该意识到 COVID-19 产生了供需冲击。由于社会疏远政策，酒店、餐馆和客运服务等依赖人员流动的行业因国内最终需求下降而受到很大影响。值得讨论的是，供应链的稳健性和弹性不仅可以抵御供应冲击，还可以抵御需求冲击。供应链的冲击传播机制在需求冲击和供应冲击的情况下是否具有相似的重要性和工作方式？公司的稳健性或关注弹性策略也将取决于冲击的来源。Todo 和 Inoue 可以进一步讨论这个问题。