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But when bitcoin crashes and we are only affected in terms of value in fiat it is not a loss because the bitcoin we have is still the same in terms of amount only the value has shrunk so it is not a loss in my opinion and I still don't like the word investment when it is able to lose because in the end the concept of loss in question is different.
The concept of loss you mean is more about losses that result from Bitcoin market fluctuations, while losses can come from anywhere.
As you said about hacking, that will result in losses that will never be able to return again.
While it is a loss because the price keeps falling, it will only be a loss when you sell it.
Those losses are an evil that cannot be reversed. That is, if you make an investment and it becomes devalued, like the price of Bitcoin would have decreased a lot, then it is not a loss, but it is there in the same amount, only the price has decreased. If the price moves up, he will automatically return his share to you and also give you a profit. The real loss is, as you mentioned, that a wallet is hacked or a coin in which you invest, and it rug pulls and steals your funds like Tera Luna did. There are many other works that can cause you real loss, i.e., you cannot return them.
So what is meant is that if you suffer a loss due to price fluctuation in Bitcoin, it is reversible; it is not called a loss. And if Bitcoin loses your affordable investment, it gives you the possibility of a return. And if there is an investment in coins other than Bitcoin, hacking, etc., then it is impossible to return them.
So invest as much money as you can afford to lose, i.e., in return.