Every possession has consequential costs of ownership. The classic example is a free puppy. There's no initial cost, but you have to feed it, take it to the vet, and make arrangements to care for it when you are away.

Every possession has to be stored, maintained, possibly transported, and ultimately disposed properly. Some possessions may be taxed. If you buy something on credit, you'll have to pay back the loan, with interest. (Worse, getting rid of the possession won't necessarily make the loan go away.)

Obviously, you don't want to acquire things that have consequential costs you're unwilling to pay.

If you want to tour on a bike and travel on a whim, you want all your possessions to be lightweight and fit in your saddlebags.

If you want to homestead an acreage and be somewhat self sufficient, you want gardens, livestock, storage sheds and plenty of useful tools, but you have to be okay with caring for all the plants & animals daily and rarely being able to leave the place for more than a day at a time.

If you want to sojourn a while in the realm of mind or spirit, you might want no possessions at all as they may distract from your meditations. Some classic examples are the philosopher Diogenes and the mathematician Paul Erdős.

My point is that the required simplicity is different from one person to another. But in all cases, simple living requires that the person make a mindful decision about which possessions are worth owning.

One big complication is that people occasionally change their minds about what kind of lives they want to lead. I think this is not at all unusual. In the past I've discarded things when transitioning from one kind of life to another, then years later I'd wish I had them back. I don't really know the wisest way to handle that problem.