Barring any significant emotional or cognitive difficulties, of course trading can be learned. As with any other vocation, it requires a certain amount of insight and skill. I think that part of the problem lies in the fact that most market participants want to be able to trade pretty much on the fly, with little or no preparation. Most other vocations are not approached in quite the same way, be it stenography, plumbing or neurosurgery. For some reason, many people with some savings seem to believe they can trade...just like that. Or they may read a few books or foolishly attend seminars and feel that they have the matter in hand. Or they might even spend a few years at it and decide it cannot be done.
Trading can be a difficult and stressful business at times. It requires a lot of time and a lot of effort to become proficient at it for the majority of people. However, I suspect that this is not what the majority of people had in mind when they decided to play the markets. If the majority of people were as flippant in other occupations as most seem to be in trading, then I think that those other professions would also have much higher failure rates. A lot of folks complain that they have been trying "hard." I would be willing to bet that many of those people probably don't know what "hard" really is. A reality check with the demands of other high-potential occupations may be in order to make sure we're comparing apples with apples.
I had a friend some years ago who is far more intelligent than I am. His IQ (for those who care about such things) is in the 140s, and he is a professor of electrical engineering at a prestigious university. He has won numerous teaching awards and is known throughout the world for his expertise in the field of electromagnetics. Further, he is one of the most emotionally stable people I ever knew. At around the same time that I began taking an interest in trading and the markets, he became somewhat interested as well. He studied the markets for a while (over the course of a few months in his spare time) and tried his hand at it. He lost money. Then he lost some more. Not long after, he became discouraged. I have no doubt whatsoever that if he had continued in his efforts and not started trading prematurely, that he would have succeeded eventually. But he did not apply the dedication to trading that he applied to his occupation. He was looking for something relatively quick, in his spare time. Trading is a skill that can be learned, but it is not an easy skill to learn. Some learn better than others and some learn faster than others, just as in any field. Those who underestimate the challenge of their chosen field seldom do well.
The thing that pisses me off more than anything else is the BS assertion that traders are "born." Everyone alive today was born. I remember the time when I was an account management trainee in corporate banking in the 1980s at Canada's largest bank. Two assholes were in charge of my on-the-job training. They held the self-important view that, because of the myriad responsibilities of the account management position, account managers were born and not made. Well, in due course, one of these "naturals" was fired and the other was demoted. I think that once people start to view themselves that way, they should dust off their toboggan to get ready for the ride down. As history repeatedly shows, self-aggrandizement is a sure step on the road to oblivion.
In summary, barring any significant emotional or cognitive difficulties, trading is a skill that can be learned. Some learn better than others and some learn faster than others, just as in any field.