It is hard to lose money in the stock market?

When you see the topic, "It is hard to lose money in the stock market", do you believe?

Let's think this way. If you have a trading method, and you lose money on this trading method, then you just do the opposite and you can win.

So it is hard to lose money.

Also, it is hard to beat the market, say the return of S&P 500 index. Look at this,
http://tony2007.blogspot.com/2007/03/secrets-about-s-500-index-that-you.html