Never really been a fan of positive thinking euphemisms but few are more applicable to trading than this one. After all, how much can you learn from a winning trade? You may have made a profit but that might simply have been fluke. A losing trade can hold a wealth of information from which you can understand how the next trade might be improved.
Recently someone asked which style of trading might be easier; swing trading or scalping. The concept of both is simple, the profitable application of either is far from easy. However, losing trades from either trading style will offer great insight. If you know your edge/method/strategy is correct but your results conflict, you know to direct your focus towards market assessment and your entries.
In this tech driven world, data is king. Collecting, correlating and dissecting your own data is crucial to success. Never let a loser pass you by without knowing the error behind it. Usually, the smallest tweaks make the greatest difference.