It’s not impossible to stay alive by yourself, with no other human resources to help you. It can be done. It has been done. People have survived, alone, in the middle of the wilderness since the dawn of mankind. That was once the way of the world. People were raised to develop the knowledge and skills needed to live off the land.
However, for a developed and modern place like present-day America, almost none of us have the skills, knowledge, physical capabilities, or frame of mind to suddenly begin fending 100% for ourselves. Most of us can’t do it, and most of us wouldn’t want to do it. We’re accustomed to our way of life full of structure and modern conveniences. We eat food that other people harvested, in homes that other people built. We drive to work in a car that took thousands of people to create and we plug away at our job where we are a tiny part of a larger operation. Sure, we still have blacksmiths and lumberjacks and true tradesmen. But the majority of Americans make a living from being a cog in the machine.