/bWhy is it hard to take a loss?
the loss is not anticipated, and comes as a total surprise, and shakes the mental foundations and confidence, the loss on average is much larger then the minute to minute fluctuations. Thus when trading, the trader feels it would be prudent to wait for it to retrace a little before registering loss.
/bWhy is it hard to let a win run?
the ability to register a win in a account even though small, induces a sense of overconfidence in the trader, so the trader registers small wins instead of letting it run. The win is not anticipated either similar to a loss, so the surprise reward makes one want to push the button earlier.