A traders methodology changes over time alongside ever changing market conditions.
A good and complete system have mastered all market conditions, so it doesn't need to change. IMO.
The only constant is you which is why I believe you must practice self discipline in all aspects of your life. If you learn to manage self discipline and emotions then you will be able to remain consistent with whatever methodology or system you choose to implement.
Yes. All this is important and it's easier to be disciplined and keep your emotions in check if you have a system with a positive expectancy and know what you're doing with confidence.
I believe more often than not the actual problem is lack of a proper system which results in personal issues and emotions.
Too much leverage and 'having to make money' also amplifies these issues.

