Consciousness. Reality(ies) doesn’t actually exists out there¹. They are the construct that you form and manipulate inside your head. So, when you choose, or are compelled by senses, to manipulate a different set of constructs, then you’ve changed realities. This is also why we say that different individuals and groups of individuals live different subjective and social realities.

1: We have reasons to infer and believe that it actually does but ontologically speaking, it might as well don’t.