"It is not because it is so difficult that we do not try something, it is because we do not try that makes something so difficult."
Seneca (4BC - 65AC)
Because of money or the desire to excel over others, a person's own fears and greed and his ability to curtail these psychologies plays the most crucial role in his success in investing.
It simply is not possible to consistently win on every single investment!
Investing comes with the challenges of losing and, worse yet, losing streaks that the investor must sometimes be able to contend with over a long period of time.
On top of this, an investor must also be able to curtail his tendency for over-confidence in a winning streak, as this will put him in a very vulnerable situation to give back what he had just made, and, in many cases, even more - all because of the lack of discipline.
Add to this the challenges that come from an investor's social world outside of the markets, and indeed, individual psychology is one aspect of investing that any participant needs to master in order to preserve capital and be in the position to beat the markets!
Discipline is not an innate quality ...
It needs to be, and CAN be cultivated through constant practice!