lost money in stock market

I have a friend,he is older than me and he 's now working in a contruction company .He 's known stock for several months and start trading .In bull market,when all the market made money,he earn a little,so he think he can earn money from it,and start trading with bigger amount of money .But in bear market,his lack of experience pulled him down .Instead of afraid and sell all,he keeping them for hoping the rising in price,but like s boat sinking,it over .And he 's in debt . I've just known one thing: u should do nothing if u don't grasp it and control ur self