Language can give you a lot of clues as to what words originally meant, and therefore how you can apply them in your daily life. A very fascinating example is the word "without". It is most commonly used to indicate a lack of something. "Without" means "I don't have xyz".
"Without" is also the opposite of "within". It indicates anything which is outside of yourself.
So what we established so far is that "without" is not only the "lack of possession" but also what is "outside of yourself". Does it consequently mean that "within" indicates the opposite of a lack of possession aka ownership? If you ask me: Yes, yes, yes!!!
You cannot possess anything that's outside of yourself. You might function as a temporary steward for sure. But at some point, whatever you think you own will be taken from you. You could lose your belongings or they could be stolen. And even if you installed the most sophisticated safety measures to keep whatever belongings under your control, you cannot keep your eyes on your possessions all around the clock. Eventually you will die too and then you'll have to let go of whatever you thought you possessed.
You can influence what's outside of you. But you cannot control it. Many native tribes in North America understood this truth. This is also the reason why there was such a clash of cultures when the white man arrived. The idea of exterior ownership falls apart under close inspection, especially when you're in touch with your environment and with yourself. We are temporary stewards on this planet.
In many relationships, be they romantic, platonic or professional, I see the same misleading notions of exterior ownership. Many act as if they own their partner. Just because you put a ring on someone else's finger doesn't make her your possession. It might give you the illusion that it's true. But it's not. You can only fail. You can only get frustrated, angry and sad once you find out that she has a life of her own.
More than that, the desire to attain exterior possessions is symptomatic and a compensation mechanism for a lack of "inner ownership". And of course this has to be learnt. You need to discipline yourself to strengthen your "inner ownership". Strengthen the awareness about who you are, who you're not, what you want, what you don't want etc. And since in western society we're trained to look without almost exclusively, it can be a hard thing to learn. But absolutely necessary and not negotiable if you want to live a self-empowered life.
It starts with the realization: What nobody can take away from you is what's within. Your thoughts, your emotions. Focus on these. Appreciate these. Nurture these. You will be truly rich.