Greed and fear are the propelling force
Pushing us to enter a trade or stay away from trading
When market condition's are unclear.
Good discipline habit can be develop over time
Some people grow up with it, some are late developer.
I think greed and fear are necessary evil to some extent to keep us motivated and being cautious with our trade.
Nobody comes into trading and succeed straight away.
The learning curve usually take more than 5 years.
I dont think discipline is the most important factor.
I believe the most important factor is actually plain good fortune to meet or recognize A true grandmaster Yoda who can point us in the right direction.
Unfortunately, grandmaster yoda is rare to find. Even when you discover them. They may deem you unworthy to learn about the way of the force. For fear of you falling over to the darkside and cause tremendous harm to humanity.
Some people are simply born with a strong force like analkin skywalker and destined to become darth vader at some point.
In a nutshell, the most determining factor is actually the real stuff mentor who can guide us in the most accurate direction possible for us to really succed at trading.