He thought briefly and said "It would be unpredictable." This answer is no less than 100-year-old. It was given by J P Morgan. Also, this answer is genuine even today, and will dependably be true.
After all costs is a function of trade charge, demand, supply, charge of cash over the world, and so on and so on. Since none of this is static, markets would dependably be unstable.
If you don't need instability, you have to spend into PPF.
There is an old Indian saying 'You can't bathe in the sea but you sit tight for the waves to stop'.
So condition you need to profit in Stocks, you have to comprehend instability and attempt to make it your friend.
Investing in Shares? Study unpredictability primary