This is the viewpoint of much of Eastern philosophy, and of The Perennial Philosophy in the West.
The starting point is idealism -- that thought is the basis for reality. This can be inferred from observation and reasoning -- we know we have thoughts, we only infer the existence of a physical world around us. Thought is primary in our epistemology, and it is reasonable to infer its primacy in ontology too.
Then one follows this idealist presupposition, with observational data from mysticism -- most eastern mystics report experiencing a "Mind at Large" or the equivalent in non-Perennial Philosophy language. IE the universe is inhabited by a massive thought, and our physical world is an emanation of that thought.
These mystics also report that they experience the release from "maya" -- the delusion of separation. Maya has different specific meanings in different eastern traditions, but a common theme among them, is that our SELF is not in realty any different from the Self of the universe.
Hence "I" am the universe.
Most western philosophy does not accept the starting premises used in this reasoning path. It is the nature of philosophy, that we can't actually prove, or validate, our starting premises and epistemological methodologies -- other than by pointing to the utility of the resulting philosophical product. That is why different branches of philosophy are all over the map on all sorts of questions.
When one cannot reach agreement on starting assumptions, and basic metrics of validity, one will have difficulty arriving at any consensus. That is why it is difficult to say whether any viewpoint in philosophy is actually correct or wrong.
An alternative approach to take, rather than right/wrong, is to accept that there are plural interesting and useful approaches to philosophy. Try to understand how different philosophic schools operate, and try to understand the value that each offers for particular types of problems.