Objects exist only within subjects' minds.
That is, there is no user26567 (it's your username on this group) for nature. For an electron or for a banana, there is no user26567. You can only exist in other people's minds.
In the present interaction, you and me discussing, the object user26567 exists in the mind of the subject RodolfoAP. If you answer my comment, I (the subject, from my perspective) will read it tomorrow and I will remember you (an object, from my perspective).
This means that a subject remembers (memory and knowledge) other persons (objects), and therefore it can interact with them. In the memory of most human subjects, there are objects (electrons, cars, bananas, shirts and other people) and a very important exception: he, himself as an object. That means that me, as a subject, remember you as an object and also remember me myself as an object. That is what makes me me. It is just my subjective memory. Although I change all the time, for my mind I keep being the same. This idea is easy to grasp with a river: although the river changes all the time, it is the same for me; has the same name, same location, same color, etc.
The initial statement (objects exist only within subjects' minds) is what an old group of philosophers called the empiricists suggested, John Locke, David Hume, George Berkeley. If you feel keen on the subject, you can read some introductions to their ideas, later refined by Immanuel Kant, although this last is really complex to read directly, without someone to guide you.