It depends upon the markets. Changing markets flush out the one-two trick ponies. Right now there are a lot of them. The directional bias has been strong for over a decade. The "crowd" trade is in vogue now. So as you allude to, the key is a variety of market conditions is required to make an accurate assessment. Risk management, money management, psychological management will all come more into play. If you don't have these, it will be a tough road. These are the things that need to be learned, IN ALL MARKET CONDITIONS. Sometimes they are only learned by getting chopped up or black swan roasted. Heck even a gray swan will "cook your goose" for a lot.
Perhaps OP can give some example of how people blow up, or just get ground up and how they teach not to do it. E.g how a medium strong, martingale strategy ends.
Thanks and good points Bad_Badness!
If anyone read the vantagepointtrading article carefully, these facts/numbers are true about the trading rate of success:
The chance of success for an untrained person is ZERO!
It reminds me of these Youtube video series

PART 1 - Top 10 Idiots Who Challenged Professional Fighters
Those who get some short training in prop shops may have a chance of 4.5% success!
I was getting these low rates of success from my students when my teaching was knowledge-based (Book/Videos/Webinars,...) at the beginning and not using Deliberate Practice with smart Drills!