The discussion is not about how to remain positive, but the benefits of remaining positive. Since future largely continues to be outside our direct control (we can influence the future outcomes, but we definitely don't control them), the only thing we can control is how our outlook and attitude remain: positive or not-positive.
By not remaining positive either we hope to win lottery or worse face doom and gloom. However, by remaining positive we either continue to have the will to strive hard, find our way out of the gloom or we find a win-win situation and enjoy our well earned pay-day. At the very least, we can try to move from Quadrant A to Quadrant B and from Quadrant D to Quadrant C.