True, if we use borrowed money for something that does not guarantee success, it is not wise.
Wise or not depends on how the person manages the borrowing money.
Sure, no guarantee of success in crypto. Even I never know if there is an investment that has a guarantee of success.
If the person is a professional trader or an experienced investor, I think it is no problem to borrow money. At least, he knows well how to trade or invest properly in crypto. And he must know the safest way to use that money. And if he can get the profits, just prioritize to pay off debt/loan first. Then, the remaining money from the profits, can be used again to rebuy another coin.
Yes, it is wise or not depending on how it is managed. And in the context here the person uses it for investment or trading, and I don't think that's good. Even if I have to make a choice, I'd rather sell a few things to invest rather than borrow. Because it's clearly our own asset, even though the worst risk is loss, we don't have to think about returning the money to anyone.