I have learned my lesson. If you sell, say R1M after a 50% gain and you are in the 40% tax bracket, you will pay an amount of R193 600 tax on your R500k gains after the R16k costs as it will be revenue.
Now as you probably do not have the extra cash on hand, you will withdraw the money from your cash account at your broker to pay SARS. This will leave you with R806 400 in your investment account. A loss of just under 20%.
If you expect the market will drop by more than 20%, then by all means, sell.
I will hold even though I know the VIX is high.