I haven't written much recently, due to low energy... Which made me realise that, all in all, there comes a limit to survival...
Energy.
Which, in engineering terms, is the ability to do work. You want to do something, you need to have the energy to do it... Gardening, keeping yourself alive... keeping other people alive, rebuilding. The reason that the developed world has been able to do so much is that energy has been readily available for the past couple of hundred years. Unfortunately, it means that we have also been going through resources in a major way - oil deposits laid down over millenia get gobbled through in decades. Metal ore deposits get pulled out of the ground as quickly as they can be found.
Don't think I'm getting all Militant Greenie, though... There is a point - it will get harder to do more. Oil, coal, gas will get harder to obtain, more work has to be done to get raw materials. Which makes rebuilding harder to do.
Or, at least, rebuilding as come before.
Maybe a chance to wipe the slate clean will be providential. There's a lot of technology that does not need to be redeveloped, if enough of the knowledge can be preserved. Plastics can be made using materials other than drilled oil. A lot of things are solved problems, but you have to know the directions that you are going in, even then things aren't always doing to go to plan. And it requires you to have enough security to rebuild, people to help...
It takes energy to do work to create energy. You can only hope that, at the end of the day, you are able to produce more than you use.