"Just because you made money doesn't mean you were right, and just because you lost money doesn't mean you were wrong. It is all a matter of probabilities. If you take a bet that has an 80 percent probability of winning, and you lose, it doesn't mean it was a wrong choice." – Tom Claugus
You have to find out a system which should be competent enough to produce your winning trades larger than your losing trades or should produce more winner than losers in long run and matter can be rest here only. Some people will make money when they will be right for 6o percent times during their trades whereas other will make money even they are 30 or 40 percent times right only on the basis that their risk to reward is more than 1:2 time.
Not the best of the best money managers in the world can predict with the hundred percent surety that which trade is going to make money for them but some how with their experience and competent systems they know that when they should put the trade and when it is the perfect time to get out of the trade whether they were right or wrong. As Tom Claugus said in his interview that If you take a bet that has an 80 percent probability of winning, and you lose, it does not mean it was wrong choice because if probability is going to same with every coming trade then eventually a trader/investor will be come out as a winner in the end.