Task: Identify the primary emotion conveyed in the tweet and assign it to either 'neutral or no emotion' or one or more of the provided emotions (anger, anticipation, disgust, fear, joy, love, optimism, pessimism, sadness, surprise, trust) that best capture the tweeter's mental state.
Tweet: The word happiness would lose its meaning if it were not balanced by sadness.
This tweet contains emotions: 
anticipation, joy, optimism, sadness