This is a lesson to the newbies that you never risk more than a small % of your winnings on a given day.
I think this is incorrect. You should never risk more than a small percentageof your bankroll, but your winnings should not have anything to do with how much you are risking. Otherwise, what would you do if you break even after the first days - stop betting?
Bankroll management is very important, but if (that's a big if!) you are really confident in your picks there's no reason not to risk all of your winnings and more as long as you stay within the bankroll management guidelines.