Trust your instincts...

Everybody says "Trust your instincts", and i do trust my instincts. But the question here arises is how to distinguish between the "instinct" and the other voices in your head? These voice could be our optimism or pessimism or simply what you really wish to happen. So how to tell that the voice that's whispering in your head is your instinct and not something else? A voice in my head, at this time, is screaming that something nice is going to happen, but how do I know that it's the instinct that needs to be trusted, and not what I really wish to happen. Only time would tell what it was.