Everybody does a mistake especially when speculating. Buying bitcoin in ATH price surely seems like a burden but if we take things into perspective and build a strategy then we can cut the loss and hence lower the burden.

I have seen people buying at ATH complaining about their losses but there are others as well who don't complaint and rather "do something" to minimize their losses. If your friend has bought bitcoin at ATH then he can do the following

1. Minimize his loss
2. Wait for bitcoin to go to moon (would probably take a long time - you never know though) - Hence not recommended

There are multiple ways to mininmize the loss such as averaging down the buying price by buying more in lower prices, trading actively so that the overall unrealized gains are increased, short term trading etc.. But these still requires skills and have risk of more loss. So think wisely and decide according by doing a good research.

This is what the fomo do cause. Although nothing has spoilt anyway. Your friend should hodl his bitcoin pretty hard, there's much hope for bitcoin to go up against $19k.

If that bitcoin price was skyrocketing more, above that $19k in 2018 till now. You could have imagine how rich he would have been by now.

The best advice is of course hold the bitcoin that your friend have, because as long as your friend's bitcoin has not been sold, your friend
has not lost money. I am also one of the people who bought bitcoin when the price of bitcoin was at $ 19k, so until now I am still holding
the bitcoin. Actually we do not need to worry about the price of bitcoin which has not yet returned to the price of all time high, because
I am sure the price bitcoin can exceed $ 19k. All we need to do is be patient, I'm sure in 2-3 years bitcoin can reach a price of $ 50k.

That's really a huge loss for him, but always think positive and never think of giving up, especially in cryptocurrency. We all know that bitcoin is volatile and if it reached that all time high in 2018 or 2017, there's a possibility that it can reach that again or surpass that price. Bitcoin is really unpredictable and I know that there are a lot of people like you who are still hoping for the better results of their investment. Never lose hope, or as soon as possible, manipulate your money or invest to an altcoins where you can have a side-line profits. There are a lot of things that you can make as a source of profit not only in bitcoin, but always prioritize bitcoin above else.

If I was among btc ath investors, my only option is to continue to hodl, I will just forget about them in a secured wallet for long term, we have heard great predictions about what btc price could be in few more years, it is possible btc will go even higher that the 20k ATH, if you are not desperately in need of money then hold.

Yours isn't same with the guy in OP's story. He bought higher at ATH and low price is far below his price. But for yours, at $400-600, you are still in huge profit. At least profit of $8800 or close there. That you didn't at ATH, doesn't mean you are now at loss.

Quite honestly he has no other option but to keep holding, he had a chance to sell his coins for a small loss back in the day but he did not took it, if he was able to keep holding his coins even when the price was very close to 3000 then it does not make a lot of sense to sell at 9000 unless it is because of an emergency, obviously this brings the question about how long he will still have to hold to at least recover his money? And that is something no one really knows as many circumstances need to come together to produce a bull market.

Many burned a big hole in their finance by investing when the price was high and when the market started falling many accounts were wiped clean because many were forced to clear their debt and if they are holding the coins then the wait to level off the entry is painstaking.

 It is not a similar position by any stretch as you are in huge profit and the OP is talking about investors who are at a heavy loss. If you are able to hold for a couple of years then you might reach those valuation but it all depends upon the global economic situation.

Actually it depends on the target of your friend. If he plans to keep it a long time, then he doesn't need to do anything unless to keep holding until the price can be above $19,000. The problem is when your friend needs urgent money in a big amount, so he should sell the Bitcoin at any price. But, if he has enough money and not needed to sell the Bitcoin, I suggest HODL strategy. Of course, it is not easy to hold Bitcoin for a long time, it needs a strong belief and a calm mind. However, if you trust in Bitcoin, you won't doubt it to keep a long time.