I agree that these traders who are unable to predict the market movement are just wanna - be traders. These are the traders that never do their assignments like studying and researching factors that will affect the movement of price value of their holdings. They are just in for the gossip on rumors that will eventually lead them to a loss.
On the other hand Real Traders can possibly predict the movement of trades. They spend their time analyzing and researching stuff about different stocks and keep them updated on news and happenings around their stocks. This traders are able to predict the next "hot" things. So I think tradings is not unpredictable instead is a predictable job.