Is financial trading a profession?

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?

What cognitive biases do we have to overcome?

What should I do if I am about to liquidate?

If you have a bad mentality, does this mean that you are not suitable for trading?

Why do successful traders not advise others to trade?