What style are you trading? What is your typical time horizon?
Right now, I'm swing trading and speculating, with a time horizon in weeks. Personally, understanding _why_ I took a position helps me to hang in there when it moves against me. If I've done the hard work of studying a trade, have a solid thesis, and got in with a good understanding of what I'm doing, it helps me to stick to my guns when it goes red in the near term. Then the fear and hope is replaced by expectation that it will swing back to me. Even then, sometimes I am wrong--but I can look back, see what I missed, and take it as a lesson.
For example, I studied what was going on, with all the QE, money printing, grants, and liquidity being poured into the economy. I believed that this would weaken the dollar and cause inflation. I built a diversified portfolio against this thesis. Because I believed in my ideas, I was able to hang in there when it moved against me. Annualized I'm up 12% on the trade so far... but this week I needed the guts hang in!