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This is a sad story that I have heard. Through this story I want everyone to know 1 golden rule in investing is: never give financial advice to anyone. By the time you give them financial advice, you may feel like you're one step ahead of them, but if that advice is wrong, you could be the one hurting them.
I'm really sorry about your friend. He bought this bad experience very expensive. He will remember this for the rest of his life. I am sure of that.
I don't have any major advice. Buy when everyone is selling and sell when everyone is buying; one of the rules I try to apply the most. I try to buy gradually in the days when pessimism prevails in the market and there are big breaks. Then I sell what I bought while the dead cat bounce (
https://en.wikipedia.org/wiki/Dead_cat_bounce) is happening.