When the numbers are starring you in the face, you will know it.
And then you come back to a thread like this or the thousands of like it on ET, and realize that your arm is as important as your leg, and your eyes as important as your nose, etc.
Being profitable requires enormous work to hone your craft or system, and the markets love to probe for weakness no matter what it is. That's why no finite list of "good qualities" will ever encompass what is required.
Most of the answers given here are looking at it the "problem" upside down. When the problem is turned right side up, all the holes get filled naturally, with the exception of possibly Money Management, or how to change bet size based on edge. That is still an unsolved problem for me because I still don't understand how to extract a probability of success for a given trade from my systems. That probably means fixed fraction as a short term solution, but I am not sure...
nitro