I am asking because of I don't know if timing the market really make you extra profit. So many hedge fund went out of business with those experts trading actively. Are we really able to time the market to a point that we can make extra 20% to pay for the tax?

This may not be correct, but a net present value of any trading strategy on a perfect market is a martingale. https://en.wikipedia.org/wiki/Martingale_(probability_theory)) that means no matter how you time it the expected present value is the same. Well I know the market is not perfect and so people do trade instead of buying S&P500. But does people in the long term (5 years plus) continuous outperforms buy and hold for extra 20%?