Closely related, in Hayek's mind, to the undervaluation of knowledge of local and specific factors is underestimation of the role of <#57#>change<#57#> in the economy. One key difference between advocates and critics of planning concerns
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the significance and frequency of changes which will make substantial alterations of production plans necessary. Of course, if detailed economic plans could be laid down for fairly long periods in advance and then closely adhered to, so that no further economic decisions of importance would be required, the task of drawing up a comprehensive plan governing all economic activity would appear much less formidable. (Hayek, 1945, p. 523)<#88#>
Hayek ascribes to his opponents the idea that economically-relevant change is something that occurs at discrete intervals and on a fairly long time-scale, and that in between such changes the management of the productive system is a more or less mechanical task. As against this, he cites, for instance, the problem of keeping cost from rising in a competitive industry, which requires considerable day-to-day managerial energy, and he emphasises the fact that the same technical facilities may be operated at widely differing cost levels by different managements. Effective economical management requires that ``new dispositions [be] made every day in the light of circumstances not known the day before'' (Hayek, 1945, p. 524). He therefore concludes that
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central planning based on [aggregated] statistical information by its nature cannot take direct account of these circumstances of time and place, and<#89#>#tex2html_wrap_inline99# the central planner will have to find some way or other in which the decisions depending upon them can be left to the man on the spot. (<#61#>ibid<#61#>.)
Rapid adaptation to changing circumstances of time and place requires decentralisation---we can't wait for some central board to issue orders after integrating <#63#>all<#63#> knowledge.