If you read the first chapter you will read the entire book pretty much. It basically explains why sometimes getting the courage to take a trade in the first place is no difference than having a loosing trade and not closing it too early out of fear.
Read it and you will be amazed how accurate it is.
On the internet, they can also learn and understand many things about how to have good psychology in trading. I studied it for years and probably still have to learn it all the time for better mentality and self-control.
I basically agree that trading psychology will only be formed from the experience, knowledge and financial condition of the trader himself. If traders do not have other sources of income to cover their daily living expenses, then of course they will always be under pressure and difficult to control. The source of the budget also needs attention, I mean it will be very annoying if they use the loan budget for trade or investment.