It certainly is possible, people do it all the time, in various countries. Most of the time we call them "homeless", but also there are people who literally set up camp in the forest then stay there, it isn't unheard of.

The book "The Stranger in the Woods" is one such case, about a man who lived in the woods for 27 years by himself.

That said, it isn't easy, and it's harder in some countries than others, but I'd still say it's possible in many countries today, YMMV.