To quote a line from a movie "A man's got to know his limitations"
There are those who know how to make money from stocks, and those that don't. The latter should definitely just leave CPF alone to earn interest.
Of course in reality that doesn't happen and there will always be a significant number of investors who lose money in the stock market (though I am also full of respect for the 59% of CPFIS investors who made money in a bad year like 2020!)
In order for me to be able to buy STI ETF when it is undervalued, I need someone willing to buy STI ETF when it is overvalued and sell to me when its undervalued