Trading Week Preparation

How to understand the phrase "the simpler the trading system, the better"?

What is the degree of simplicity here? Or the simplicity here is not what I thought, just use a few indicators, so what do you think of this sentence?

Ask for advice on how to manage trading positions in order to achieve long-term stable profits?

A handful of bitter tears, I have been trading for five years, and I still lose money, what should I do?

I have been unable to set the stop loss in the transaction, how can I do a good stop loss?

Why can you see the general direction right, but make a bad point in the transaction, and lose money instead?