I don't think that's how the sunk cost fallacy is applied. It's more like if I booked an AirBnb that I thought was 5 stars, and it turned out when I got there that its a shitty apartment I never should have booked and paid for. I then suck it up because I already invested the money into it, rather than cut the costs to find a better AirBnb.

Or I have a gambling problem I lose all most of my money but continue to gamble because I've already invested so much into it.

Or staying in a crappy marriage because you've known this person your entire life.

For a crypto investment, putting money into a coin that deceased in price isn't necessarily a sunk cost because its so volatile, i.e., it could go up the next day. Sunk cost by definition is something that you cannot recover. He hasn't realized a loss. That's part of why tax law is the way it is - you don't get taxed until you sell for a profit.

@dave-steem : long story short, everyone is hurting right now because we're in a bearish trend. I'm not a financial adviser either, but I would wait and monitor the price action closely. Do your home work and study where the trend is going and manage your risk - only invest what you're willing to lose. The price could go up or it could go down - no one really knows, but there's a fairly high chance that you can recover barring a catastrophic crash.