Op message may be directed to those not making profit after some time in trading but the fowl part about his message is that he forgets that everyone has different years they spent developing trading skills before they started making profits. For some persons it could be 2 years, other could take 5 or more years before they get to start putting things right. So coming out straight to discourage people from venturing into trading is really bad.
I share your thoughts @Lida. OP's advice might sound correct but it's not totally true. There is I no generally acceptable duration that one should trade before he would conclude to quit or continue. We have heard motivational stories of people who failed in a field for many years. But they were determined to succeed and at the end they achieved great things. This message could discourage someone who might be destined for success in trading.
But for those who have refused to keep learning and upgrading their trading skills, they should consider leaving. This is because this field requires constant learning.