Depression is the result of an intense feeling of loss. That feeling of loss can be for something that we once had or it can be for something that we hoped for.
When we’re depressed, we’re using our imagination to make ourselves feel unhappy. We’re remembering what once was (probably inaccurately) and we’re projecting what could have been (probably inaccurately), and it makes us feel terrible. It makes us feel like life is unfair—even pointless.
If we were to live in the moment instead, we would realize that things aren’t nearly as bad as we imagine them to be.