Task: Classify the mental state of the tweeter based on the tweet, determining if it is 'neutral or no emotion' or characterized by any of the provided emotions (anger, anticipation, disgust, fear, joy, love, optimism, pessimism, sadness, surprise, trust).
Tweet: Regret for the things we did can be tempered by time; it is regret for the things we did not do that is inconsolable. - Sydney J. Harris
This tweet contains emotions: 
pessimism, sadness