Flow is a part of something called positive psychology of the psychology of happiness. Positive psychology looks into what makes a person happy. Flow can be considered as achieving happiness or at the very least positive feelings. A study that was published in the journal "Emotion" looked at flow experienced in college students playing Tetris. The students that were being evaluated on looks then told to wait and play Tetris. There were three categories; Easy, normal, and hard. The students that played Tetris on normal level experienced flow and were less stressed about the evaluation.