You're interpreting what I'm saying (and what I believe the author is saying) as "amount you won't mind losing, so just go for it bro, you might hit it big!"

Maybe I'm reading too much into the original text, but when I said, "amount you can afford to lose," I intended an implicit "because you will lose it and then you will learn" that I think the author is also implying.

If you do a 9 week fake money stock pick'em exercise (say in a FINA class), people will follow it for exactly 9 weeks, some will lose, some will win, and everybody who doesn't win will take away "gee I should have picked better, that was obvious in retrospect" which obviously isn't the point.

With real money, I feel like you're more likely to learn the intended lesson. If it works out for nine weeks, you'll keep at it because it's actual money. You'll learn eventually.