Discipline according to Wikipedia is the assertion of willpower over more base desires, and is usually understood to be synonymous with self-control. 

In working with hundreds of traders over the years I see this quality as the major key to being a successful trader.  99.99% of all traders will take a top notch setup and see a big profit added to their balance. 

A LION STALKING ITS PREY

The hard part is being disciplined when you don’t see a good set-up and you settle for a low grade set-up that has low odds of working.  It is the trades you don’t take that make you wealthy.  If you could sit at your trading desk and imagine you are a lion waiting for the best prey to come across the field.  The lion sits and patiently waits for its prey. 

While waiting for its prey, it does not jump on a tiny mouse for dinner.  Your job as a trader is to wait until the best set-ups come across the screen and then you pounce.  Everyone is good at taking the good setups that work and pay well.   It’s the times where the market is not providing any good set-ups and you’re scanning for hours and not seeing a thing to do. 

That’s when you get tempted to take the low grade scraps for dinner because you think it can pay you something.  I run a trading room as the head moderator and I tell my traders I wake up with this mindset, “I am willing to not take a trade today if I don’t see a set-up.”  I want to see set-ups where I have to say to myself, “I cannot pass this up.  It fits my trading plan and it’s a top notch set-up that I have a high batting average with.” 

LET YOUR MISTAKES HELP YOU LEARN

In the career path as a trader the market provides you with a learning curve.  Don’t work against it but rather work with it.  Let pain be the best school master you can have.  My traders say to me, “you’re the most disciplined trader I know.”  My response to them is, “I have been doing this for many years and pain was a school master that taught why I should sit out this set-up.”  Learn from the pains of your mistakes and use them as fuel to become a better, disciplined trader.