Phil Oliver states a truism:

Happiness is more likely to flow from simplicity and richness of experience than from the accumulation of material possessions.

But Steve Hagen preemptively asked exactly what we mean when we talk about “simplicity”:

I once spoke at a retreat in which people had gathered to examine, among other things, the idea of simplicity — more precisely, living the “simple life”. One of the speakers was a woman who had spent a number of years living in the countryside in Wisconsin, raising a family. Many years ago, she and her husband decided that they would go off to the country and live a simple life. By choice they didn’t have a phone. They didn’t have electricity. They didn’t have plumbing. They raised two children. And they surely led a simple life because, having so limited their activity, they made few demands upon their environment and upon the world.

Most of us at the retreat probably had a clear sense of what is meant by a “simple life”. It meant living unpretentiously, humbly, and efficiently; above all, it meant being self-sufficient and not tied into or dependent on some massive, external “infrastructure”. Yes, we all knew what the simple life was, even those of us who didn’t live so “simply”. But as we discussed the idea of simplicity, we began to see a great deal of complexity in it. After all, here were our friends, clearly leading a simple life – we all recognized that they did – but when it was time to do the dishes, they had to have already cut some firewood, which had to already have been cured and hauled into the house. They then had to stoke a fire, pump their water from the well, heat the water on the stove, pour it into a pan, and regulate its temperature by mixing it with more cool water from the well. Then they could do their dishes — after adding some homemade soap.
By contrast, those of us who don’t live quite this “simply” load our dishes into the dishwasher, add store-bought soap and push a button. Yet we most often think of the lifestyle which includes a dishwasher as being the more hectic and complicated one. We call the first lifestyle the simple life, the second a rat race. But where’s the simplicity? Where’s the complexity? Clearly they are two. But if they are two, how are they two?
I’ve known people who quit the rat race to go live on a hippie commune or take up some similar kind of back-to-basics lifestyle, only to still be plagued by the same old frustrations and unhappiness, which always told me that simplicity was a state of mind, not necessarily related to external circumstances. You can find contentment almost anywhere, but if you don’t already have it in your mind, sitting in a cabin in the woods with nothing to do but grow and prepare your food, among other menial chores, isn’t going to magically make you feel that way, especially once the novelty wears off. Self-sufficiency itself is one of the biggest illusions there is. You’d think more reflective people would realize this, given as they are to contemplating the myriad ways all things are connected.