Most traders focus too much on the outcome of the trade they are currently in. This is a big mistake and the source of most unnecessary trading losses.
Each trade should be seen as one trade of the next twenty or fifty the trader is going to make. Many of those will be losses, but many will be winners. The results of those bigger sequences—and not the trade-by-trade outcomes—are what really matter.
(this is an excerpt from the Trading eCourse: Chapter 3 - The Mental Game, section 3.4 - How to Think about Individual Trades)