Consider the following scenarios:
*  We decide to enter a position at a particular price level, it hits that level, and we create an excuse and fail to take advantage of an opportunity;
*  We set a stop loss on a position, but rationalize staying in the position when that level is hit, creating a loss that wipes out many days of gains;
*  We establish a process for researching markets and keeping ourselves in peak condition, but become distracted by life events and fail to follow our process;
*  We take an unplanned trade after losing money and widen our losses.
In each of these cases, we have what traders commonly call a loss of discipline.  In fact, it is a failure of willpower:  an inability to sustain intention.
Our focused attention–our intentionality–is a finite resource.  It becomes fatigued with use.  When we frame trading problems as one of lack of discipline, we treat our challenges as character flaws.  When we frame trading problems as one of lack of willpower, we open the door to strategies that preserve the willpower we possess and expand our level of willpower over time.