There are three things:
 
1) Having an edge, which is some methodology for determining with reasonable accuracy the relative probability of the market price hitting your profit target before it hits your stop loss price.  An edge is provided by a set of trading strategies, and a set of rules for when to use which trading strategies (briefly, when to follow a trend, when to fade a trend, and when to stay out.)
 
2) The discipline and emotional fortitude to follow the rules of your trading rules flawlessly.
 
3) Sound risk and money management rules.  
 
Sound money management and risk control are the keys to being a profitable trader. It is not the prediction or the latest and greatest indicator that makes the profit in trading, it is how you apply sound trading discipline with superior cash management and risk control that makes the difference between success and failure. 
 
Consider the story of a great restaurant that opens up at a great location. It opens with great fanfare and gets ranked in the top five restaurants in the city. The food is outstanding. But it only takes a little more than a year and this great restaurant will be out of business. Why?  Because the key to running a good restaurant is not the food…it is cash management and risk control. It is making sure your business is run efficiently, keeping your costs (risk) in control, and managing your staff effectively. If you believe that the taste of the food is what makes a great restaurant, think of how great the food is at your favorite fast food restaurant. But, someday, watch how well that restaurant is run. 
 
Just as in the restaurant business, the key to profits in trading is not in the prediction or the indicator, but how well the trading strategy is designed and executed. The ability to achieve risk control and cash management will make the difference between a successful trader and an unsuccessful trader. If you ever have the opportunity to watch a successful trader, you will see that they worry more about risk and money management than they do about where the market is going or about predicting when the next big move will take place. They aren’t looking to tweak their indicator. They are worried about their risk on each trade. Is the trade being executed correctly? How much of their total account is at risk? Are their stop loss orders set at the right price? At the price where it’s reasonably clear the market will probably move much further against them?  Is their position size appropriate to their account balance and the maximum loss they might incur, based on the price where their initial stop loss order would get them out of the trade (at a loss)? It’s getting those things right that makes or breaks a trader over many trades.