Space has a Tendency to Fill Itself
An average US household has 300,000 items. I would argue that it's a lot. But looking at my own childhood in Finland, it's actually not surprising. We tend to gather a lot of stuff. And there's a perfectly reasonable explanation for it: space has a tendency to fill itself.
How many times have you packed something and noticed that there's still a little bit room in a box or a suitcase? And then you started thinking what more could you fit in since you have all this extra space. I have found myself thinking about that a lot. When I started decluttering my stuff, I caught myself multiple times thinking "I'll give myself this box for board games, everything that doesn't fit in has to go." Once you start going down that path, you will eventually fill every space you can find.
The Space #
How about you start thinking from a different perspective? Instead of finding an apartment or a house and thinking about how to fill it, start thinking about what you need and love to have and find a place that fits those. Or first gather your belongings for a trip and then find a suitable case or bag for them.
It's not easy. Even after a year I still find myself thinking from the perspective of the space and not so much from the perspective of the needs. If you live alone, do you really need 8 large plates, 8 small plates, 8 bowls and 8 champagne glasses? When was the last time you actually used all of them at the same time? If you regularly host dinner parties, great, keep them. If not, I suggest you think about why you own so much. That example is from my life. The only effect that having 8 of each had was that my sink was always full of dirty dishes.
I'm now 30 and for the entirety of my adult life, I have moved into apartments first and started thinking how can I fill them after that. Only recently have I started to slow down and actually think about what I want and need first. That's why I'm currently living a domestic nomadic lifestyle, living 3-4 weeks per apartment as my friends travel until I can figure out what I actually want. But that's a story for another time.