As we evolved and developed into hunter-gatherers, there was a reward system set up in our very being and it's not being fulfilled by modern society and it's one of the things that is causing depression.

We're living our lives in very unfulfilling ways. We're sitting in boxes with artificial lights and do things we don't want to do only to end up mentally exhausted. Meanwhile we're eating shit. We're eating potato chips and drinking soda and our bodies are screaming "What the fuck is this? We're supposed to be out in the fields, walking up hills, looking for animals and gathering plants. We're supposed to be in nature!" and nature is like a medicine.

Just go hike ontop of a mountain and look out, there will be a reward that is intensely soul-filling.