Because as the time is extended, the possibility for things to get critically out of balance increases, possibly exponentially. This is not merely sitting a co

Because as the time is extended, the possibility for things to get critically out of balance increases, possibly exponentially. This is not merely sitting a coated steel bar on your shelf and expecting it to not rust. It is a highly dynamic cycle of multiple feedback loops and organizims, especially the soil microbiota. Any of it goes off, and the whole thing could collapse, and it could take a long time for that to go critical. In this very example, he presumably determined tha tit needed water after several years, but added enough to balance to system so it lasted in a sealed condition for 47 more years.