not true.
say you had a losing trader/ losing sytem and you did the opposite of his entries its still possible you would lose after you take into account costs.
Say you are a Forex trader (as many retail traders are) and you pay a 2 pip spread on cable. Thats costing you $2 everytime you trade assuming you are using standard $10,000 positions (again to keep this in the context of retail traders). Assume you do 7 trades a day, which again I think is in keeping with most retail traders you are spending $14 a day just to trade.
Say you do this for 50 weeks of the year you have to have made 3500 ticks over the course of the year to break even. Or 291 a month, take into account picking whether the market will go up or down is pretty hard most people cant even make 291 ticks a month assuming there was no spread or trading commissions.
Take it up a level, (as nobody is going to get rich trading $1 a pip) and we trade a standard lot on the in interbank market which is $100,000 positions, or $10 a point, that same equation means you have to make 35k a year to stand still!
This is why success rates are higher in the professional trading community. For a start, in 6 years of trading at various firms I have never seen anyone trade cash FX and make money unless they are on a market making desk that eliminates this spread. They all trade futures and traders are paying sometimes 0.80cents to put on a trade. Or 0.08 of a tick. You could have a trader at home that is a better trader than the professional but pay retail rates and could lose tens of thousands over the course of the year whilst an average (yet positive ticks) trader at a professional firm would earn a comfortable living.
making ticks is hard dont get me wrong, but the cost of doing business is what kills "most" traders