Trading is a zero-sum game; for some participants to make money, there must be less informed participants that lose money to the winning participants. The problem with this is that participants that are losing money either get smarter or faster and stop losing money, or they continue losing money and eventually exit the market altogether, which will hurt continued profitability of our trading strategies and can even get to a point where we cannot make any money at all. If our trading strategies are making money by trading against these less informed participants, and they either become better informed and stop losing money or they leave the market, either we lose our trading signal advantage that relied on their behavior, or the competition gains edge on us causing our trading strategies to go from being profitable to losing money. Intuitively, since no participant that is losing money continuously is likely to continue trading, it seems likely that this is a business that is eventually going to die out for everyone.

This doesn't happen in practice because large markets are composed of a very large number of participants with different trading strategies, different trading horizons, and different information. Also, participants exit the markets and new participants enter the markets every day, creating new opportunities for all participants to capitalize on. To summarize, since market participants are continuously evolving and new participants enter the market and existing participants leave the market, it is possible for us to lose those participants that provide the trading signals that we use in our trading strategies. To deal with this, we have to constantly search for new trading signals and diversify trading signals and strategies to capture more market participants' intentions and predict market price moves.