How to control your emotions in trading?

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?

Tell me how hard you have worked to make money in trading?

Are you happy doing business?

There is no such question, so I mention it.

What do you think are the core competitiveness of a good broker?

Do you guys have any good suggestions to save novice Huiyou like me from taking some detours?