The design of a trading system is key to investment success. An effective trading system typically includes four core elements: accurately determining the direction of market trends, formulating a clear get on board strategy, setting reasonable stop loss and profit targets, and implementing strict capital management. These elements form the foundational framework of any successful trading system.

When building a trading system, there are two points worth paying special attention to: first, even when using common technical indicators, sufficient backtesting and validation are required. Only after proving the profitability of the system in a simulated environment can it be gradually applied to actual trading. Second, the trading system should remain simple and easy to operate. Simple systems are often easier to execute strictly, and this is the key to achieving profitability.

When it comes to technical indicators, MACD (Moving Average Convergence Divergence) is undoubtedly one of the most popular tools. The reasons for its popularity are mainly as follows:

1. The MACD has been proven to be one of the most effective technical indicators through long-term market validation and is widely used in various trading strategies.

2. As a derivative of the moving average indicator EMA, MACD performs excellently in grasping trending markets and is especially suitable for trend investing.

3. The MACD divergence signals are widely regarded as the most reliable 'buy low and sell high' tool, not only praised in practice but also closely related to trend theory and wave theory.

Overall, mastering the use of the MACD indicator, combined with a reasonable trading system design, can help investors better seize market opportunities and improve trading success rates. However, it is important to remember that any trading tool and system needs to be continuously adjusted and refined in practice to adapt to the ever-changing market environment.