Most novice traders hold on to loses and let go of wins. Sounds ridiculous when you loud it yet several studies have shown that it's the most common mistake made by traders. It is simply our humanity and the completely irrational but understandable fear of loss.

The principle is simple.

When we start winning we get anxious about loosing our gains .we close trades prematurely to capture the profits before the price starts to drop again.wereas we should be holding on to it and closing appropriately to maximize the profit.
     Conversely,when we start loosing we hold on to the losing position longer in the hope it will turn upward at some point.we have the irrational beleif that we will reduce or wipe out the lose without proper re-analysis.

This is thesame principle that casinos exploit to keep unwitting patrons pulling at the one-arm bandits until their bank accounts are emptied.
  So even if we have more winning trades than losing ones, the average size of the wins versus the loses finds us in a net lose trading position over time.

It is the most basic and destructive mistake a trader can make and if left unchecked could become habits that would be difficult to break.

Please do well to add your opinions on this as this post is pron to corrections and contributions. Thank you.