Any investment can be profitable if we have sufficient knowledge, because in my opinion, some cases that occur are usually they invest but not with sufficient knowledge, sometimes they do it with minimal knowledge and losses when something like this is a natural thing. I have an older friend and he has been involved in bitcoin investment for a long time, yesterday's case where bitcoin experienced a fairly shocking price drop made him lose everything but he reinvested his money. It all depends on our mindset and the knowledge we have with what we are pursuing, if it is pursued well then the results will be positive.
I am quite curious how your friend could lose everything when he invested in Bitcoin for quite a long time, because if he has been involved in Bitcoin investment for quite a long time, of course a decline like some time ago is not the first thing he has experienced, so there should be no panic, but I suspect your friend is not an investor but a trader and may trade in Bitcoin vs Altcoin pairs, but this is just my guess. And investing with adequate knowledge is very important otherwise panic will arise when reading the news or seeing a market that is not good.