I lacked the patience and discipline required to sit through short term pullbacks in the nascent stages of my trading career and so very often I would look back on stocks that I had had positions in a few weeks or a few months earlier and say, "Why did'nt I just hold onto that?!". Now I force my self to sit through at least one pullback in stocks that move up nicely from my buy point especially in the early stages of an uptrend. I know that many times I will get stopped out. But the huge occasional winners will more than make up for the many small losses and then some leading to a much higher expectancy than I have now.
Good luck with your own trading!